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Posted by: Brian Fuerbach Mar 27 2022, 06:36 PM

1974 1.8 with L- jet. Been playing with a wide band air fuel meter and noticed that when I lift the throttle the AFR goes to max value on the gauge. I thought it was supposed to go lean. I checked the throttle position switch and it checks out fine. Going to check the wiring harness next.

What else should I check? Decel valve?

Posted by: emerygt350 Mar 27 2022, 06:44 PM

My mustang goes super lean on throttle lift, as it should. My djet does not and often does as you describe and never goes super lean on lift. I wonder how many others have observed this.

Posted by: Van B Mar 27 2022, 07:19 PM

I haven’t measured my AFR to compare so, I can’t say how mine does.

Do you ever get idle hang on deceleration i.e. it gets stuck above idle when you’re slowing down?

Posted by: Brian Fuerbach Mar 27 2022, 09:50 PM

I did have that problem in the past. One thing that helped was to adjust the decel regulator to bring the rpms down quickly to 1000 without going below. Of course this changes with engine temp so it was a balance. I switched to the 123 distributor and my transition to idle became nearly perfect. Idle is really steady now.

Posted by: Van B Mar 27 2022, 10:04 PM

Ok so, two thoughts:

1.) set your decel valve to begin opening at 20 in-hg of vacuum.

2.) Does your 123 retain it’s advance on decel? I might be wrong here but I think the OEM dual vac pulls timing on decel

Posted by: Brian Fuerbach Mar 27 2022, 10:45 PM

Good question. I have the vac capable 123 and I will have to check for sure if pulls the vac advance out on decel. I think it can be mapped to do both adv and retard but not sure. We are expecting some rain tomorrow so I will report my findings mid week. Maybe someone reading this can confirm if adv is active during decel.

Posted by: Van B Mar 28 2022, 12:29 AM

Ok, I’m too tired to think straight but yes, your timing should retard when the throttle is closed regardless of RPM.

Timing retard vacuum is pulled from the bypass port on the throttle body, which is only used when the throttle plate is closed.

Look at line B


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Posted by: wonkipop Mar 28 2022, 01:34 AM

you are not getting tired, you are getting really good.

correct on all counts.

why it would be rich....?
could be connected to that?
but i would have to think about that too.

those two ports behave slightly differently.

when throttle is fully closed the one on the manifold side of throttle plate activates retard can on distributor.

the other one, on the inlet side works at part throttle and cruise to advance the distributor.

and in typical VW fashion the advance one serves to cushion the distributors response to load.

but, its meant to lean for emissions when you close off throttle.

i'm just trying to remember how it goes.
might have to go back and re read manual to remind myself.
or alternatively clay perrine can just come in and say it in 5 words or less.

but i know the fuel pressure regulator does a bit at that point too.
backs off the fuel pressure - because its linked by vacuum to the plenum as well.
there is that t connection to the same vac line as the decel valve.
and there is something else that goes on with L jet probably in the afm.

get back to you if someone smarter doesn't do it first.

------

those double can distributors are amazing.
there are f$ck all cars in aus with them.
they belong to a period in time and USA cars in particular.
i have only really got my head into them since getting mine going again.
basically its the main emissions device? sort of.
we still had just advance can distributors on VWs here from same period in time.

-------
but in a carb car we wouldn't be worried if it was going full rich on throttle off deacceleration.
we only expect it to be lean because of emissions regs and fuel injection artificial intelligence combined with cuckoo clock mechanical devices aiding it.

???

or am i wrong.
but if its behaving properly as per EPA and being L jet, yeah it should go lean.

Posted by: emerygt350 Mar 28 2022, 08:43 AM

But here he is running a 123 right? so you have to choose retard or advance. My rich on lift didn't change when I switched from retard to advance (and moved the vacuum line appropriately).

I suspect with the butterfly closed, the pcv closed (on my 73, others may not have that), that the decel valve really can't let enough air in at meaningful rpms to thin the mix much. On a 1.8 I bet the vacuum operated fuel regulator (it is vacuum on the 1.8 right?) is a critical part of the lean on lift. Wonder if you have some issue there?

Posted by: Van B Mar 28 2022, 09:13 AM

Definitely possible.
As you've seen through my quests, the air from the decel valve is still measured air since it pulls from the intake boot after the AFM barn door. If the decel valve is flowing air when it shouldn't be, then the AFM will fuel the engine. I'm thinking maybe it could be too much fuel given the throttle body is fully closed in those moments.
In my view, you only want the decel valve to open at moments of high vac... throttle chops etc.

My point about timing is that if it remains advanced when the throttle is closed, then the burn won't be right and will almost certainly show a low AFR (rich)

Posted by: Van B Mar 28 2022, 09:17 AM

Now that I think about what I just posted, I bet there is more than one cause/tuning issue at play here.

Posted by: emerygt350 Mar 28 2022, 09:24 AM

Is the AFM before or after the boot? I need to put up a diagram of these two systems. Advance should pull out as long as you have it attached to ported vacuum. Perhaps that might be an issue here? If the vacuum advance is hooked to the plenum you would end up with advance when you lift rather than during slight throttle opening.

Posted by: Van B Mar 28 2022, 09:36 AM

AFM is literally the barn door. it attaches to the air filter box and precedes everything. However, the car he's running here has two vac ports for the distributor. one for retarding and one for advancing. That's what I was showing on the page I posted. what that means is that there is progressive vac advance or no advance + vac retard and no retard.

Honestly, though, I have no clue what AFR should be expected from an L-jet at elevated RPM with a closed throttle. Without this ref we're just theorizing and having conversation for the sake of conversation lol...

Posted by: ClayPerrine Mar 28 2022, 09:48 AM

The AFM in an L-Jet system will push fuel into the ports as long as there is airflow through it. So on decel, you will have a lot of air moving through the AFM even if the flap is closed due to the engine spinning fast.

That may be causing the rich mixture you are seeing.

Clay

Posted by: emerygt350 Mar 28 2022, 10:37 AM

So a decel hooked to the boot would be unmeasured air? AFM -> Boot -> throttle body? or is it Throttle body -> AFM -> Boot? If it is the first situation, the closed throttle body should reduce flow across the AFM and result in high plenum vacuum and the decel leading to the boot would cheat the AFM. I would think you would want the decel after the throttle body to be most effective and cheat the AFM.

Posted by: emerygt350 Mar 28 2022, 10:38 AM

I believe he said he was using a 123, so just one port on the dizzy.

Posted by: Van B Mar 28 2022, 10:42 AM

Everything is measured. Remember my first thread?

http://www.914world.com/bbs2/index.php?s=&showtopic=356522&view=findpost&p=2958074

Posted by: Van B Mar 28 2022, 10:43 AM

Right. Which is why I went with pertronix instead.

Posted by: emerygt350 Mar 28 2022, 10:44 AM

Is this correct?
I know they changed stuff every month on these things.

Posted by: Van B Mar 28 2022, 10:45 AM

the little subset square on the airbox is meant to represent the AFM... poorly lol

Posted by: emerygt350 Mar 28 2022, 10:47 AM

If it is, man that doesn't make much sense to me. Why would you pull air through the AFM bypassing the throttle blades? There must be an 'on off' with the TPS. If throttle is closed, don't listen to the AFM. At that point, why not just suck it before the AFM for the decel?

Posted by: Van B Mar 28 2022, 10:56 AM

TPS really only knows when the throttle is open (not at idle) and when it's full throttle. Everything is driven by the AFM. It's a v1 MAF really.

If @http://www.914world.com/bbs2/index.php?showuser=760 can confirm the opening vac for his decel valve than that will give a clue into whether the AFM is sending extra fuel even when the throttle is closed. I'm a little skeptical about that because if the decel valve was sending air, I would expect to see rev hang i.e. very slow wind down of the engine from high RPM.

My money is on the timing. too much advance at high RPM + not enough air = incomplete burn that is picked up by the AFR.

Posted by: emerygt350 Mar 28 2022, 11:02 AM

Too much advance could certainly do it, but there should be a healthy fuel cut too. If the TPS is saying the throttle is closed, the AFM should be ignored (well, idle level), and the decel pulling air from the boot and dumping it into the plenum should (should) cause a lean mix. And add to that the vacuum on the fuel regulator. If that is all working correctly then the only thing left is advance. Or just normal behavior. Not like many of us have AFRs. Wish they were more common and less expensive..

Speaking of that, Brian, out of curiosity, where is your O2 sensor located?

Posted by: Brian Fuerbach Mar 28 2022, 01:43 PM

Regardless of the vac adv or retard, the centrifugal advance in a stock distributor will keep the advance at 27 degrees. Not sure pulling out 5 degrees timing would change the afr that much.

I will check my decel valve opening values tonight.

I am running a 2.0 Bursch exhaust. The 02 sensor is located about 10" downstream from the collector.

Posted by: emerygt350 Mar 28 2022, 02:04 PM

Yeah,we were only speculating on 'way too much' advance. Or at least I was. My O2 is in about the same spot on an Ansa setup.

Posted by: wonkipop Mar 28 2022, 03:00 PM

the throttle switch on the 1.8 operates at two positions.
idle. throttle closed.
wide open. (a position wonki occasionally enjoys torturing it with).

in between the flap in the afm does the fuel measurement (reacting to air amount).

i guess therefor fuel is metered by throttle body switch for the two extreme points.
when you snap the throttle closed the afm may be getting pulled open via the decel valve, but the fuel mix will be dictated by the throttle switch? ????

think i have that right. but happy to be corrected and unlearn something.

i'd have to think more about it precisely.
and go back and read some of the tech manuals.

i don't have a decel valve operational in mine.
and i haven't measured a/f mix on throttle closed, to know what it does.
but i suspect i don't have a rich air fuel mix on throttle closing as i don't get backfires.
ie not dumping fuel rich mix into a hot exhaust where it can detonate.
but i suppose it could still be rich, just not rich enough to backfire.

the decel is supposed to stop the engine going below idle, dying and coming back to life.
that can happen with my car, but only when still cold.
a weird thing where you snap closed the throttle and then there is a second of silence before normal service resumes.


so....the rich thing is interesting.

i don't know how fast the dist would return to full retard idle position.
its in its centrifigal phase as revs come down.
the vac can would have very little advance action going on from the port in front of the throttle blade. it would be in full retard action if hooked up properly to the retard port on the tb or to a vacuum source in the plenum. which means all the way down as revs decline the dist will be that 3-4 degrees further retarded than if it were a pure centrifigal dist. and that would be making the burn more complete. which is what the emissions oriented design is meant to do.

Posted by: r_towle Mar 28 2022, 03:06 PM

My experience with this is two things.
1) a dirty distributor advance plate area. The OEM grease is now like hard gooey plastic, and it is no longer a lubricant, its more like glue now.
Remove dizzy, take it all apart and clean it, make sure the advance plates move freely and fast. Make sure they snap into the non advance position.
Add wheel bearing grease...about 0.05 cents worth. Car will be happy.
2) you have a vacuum line plugged into the wrong place, or the wrong way.
try nothing on vacuum advance (at the dizzy) then try nothing on the retard.
If I recall, you may end up with a hose on vacuum advance, and nothing at all on the retard, just leave it open to the air.
2a) a vacuum leak with make the car have a higher idle..so that too,

Overall, the car will run with all vacuum ports closed off at the plenum, then you can add one hose at a time until you find the culprit.
Dont trust that after almost 50 years that something is not leaking, has a hairline crack (plenum) or some fitting or hose is no longer perfectly tight.

EFI is all about measured air/fuel to get it right.
You have an air issue.

Rich

Posted by: wonkipop Mar 28 2022, 03:41 PM

no. not quite emery.

the decel valve is cheating the throttle body is all that is happening.
and its pulling the flapper open as a kind of second throttle body.

the decel gets pulled open by vacuum in the plenum when the throttle is closed.
this operates an alternative route for air which is (and can only be) drawn past the flapper - and therefor operating it.

vacuum declines as revs drop and the decel gradually closes.
closing the air route.

its basically just slowing down the action of closing the throttle so its not so violent, on and off. which is why a lot of the 911 guys used to rip the decel valves off.
i think in the case of the 911 guys it was on the K jetronic system? they hated them.
they wanted violent on off throttle. (something to do with having an engine in the wrong place in the car and going around corners?).

the decel valve is operated by the same vacuum line that branches off to the fuel pressure regulator. so on decel the same vacuum opens up the fuel pressure regulator a bit more and drops fuel pressure.

which is why i am still thinking. because fuel pressure and dropping fuel pressure does come into it with L jet. exactly how it affects things i can't really say. but L jet is wanting to drop the fuel pressure on throttle closing situations.

Posted by: emerygt350 Mar 28 2022, 03:52 PM

But wonkipop, that completely ignores the ecus response to the throttle being in the closed, idle position. If that is in fact one of the signals the tps sends then at idle you would expect some kind of over ride on the afm. I may be completely wrong on that, it just seems logical since a like circuit exists in the djet. Things run differently if the throttle is closed.

Posted by: wonkipop Mar 28 2022, 03:56 PM

yes

thats the bit i am still thinking about. where i say so in above posts.

which one gets over-ridden. because one must? i agree with you.

i have to go back and read manuals to answer that.

but the throttle is in the closed position. and that definitely does say something to the ECU. where it is quite unlike D jet is that is the only time it says something to the ECU, except for the other time when you have your foot mashed into the firewall. and when you do that, it just says to the ECU, give me all the fuel you got. all of it.

and the flapper is being pulled open (sustantially so) by the decel route while the decel route is open. so does that dictate anything in air fuel mix? don't know.

Posted by: emerygt350 Mar 28 2022, 04:20 PM

I would bet it does, otherwise they would have just run it into the air cleaner pre-afm. But what does it say!!!? Perhaps the same thing it says when the aar is open? What does the fox say?

Posted by: wonkipop Mar 28 2022, 04:59 PM

here is a bit of the story emery.

i knew L jet did something where it cut off fuel.
hence the reason the fuel pressure regulator is plumbed into plenum vacuum along iwth decel.

we like to joke about these things being from the jurassic age.
but really its the ice ages and wooly mammoth era.

carbies were around with t-rex.

there is a bit of talking going on to the old lunar module era ECU and it can sort of think in a preconditioned pregrogrammed routine way.
its getting sensor information also from the dizzy to tell it what is going on during coasting after throttle closes.




so if you come off revs with the engine spinning fast enough it knows what is going on.
cuts off fuel until a certain point where revs are low enough and resumes supply despite throttle switch being at idle position. so there is a primitive neuron dedicated to that input.

must be similar with decel valve. knows that if flap is being pulled open a certain amount but throttle switch is in idle position then its got to do the decel thing and another neuron flashes on and does that routine.

so not exactly an overide, more a response to very particular environmental inputs.

its dumb, but kind of like a three year old or a chimpanzee. pick up the red box and you can have a peanut sort of thing.

still can't answer the fuel rich thing on deacceleration exactly.
but in a standard L jet set up with the original dizzy, there are a few things going on.
and all of them are really leaning it out. first no fuel. then some fuel and some air to stop it dying in its tracks (the decel valve) and then finally we are idle revs and it settling down.

but i had remembered right about the fuel cutting off. and i think it does it quite differently with D Jet but again i just know its different, but not how its different because i don't do D jet.

Posted by: emerygt350 Mar 28 2022, 05:09 PM

It would be interesting to know what the dizzy connection is since in this case we have a 123 rather than the original.

Posted by: Van B Mar 28 2022, 05:16 PM

You might want to check this chart, we’re not talking about just 5 degrees

74 model would be using 205 AA


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Posted by: wonkipop Mar 28 2022, 05:53 PM

yes.


anyway

Van is right. it is retarding with the original dist so thats doing a later burn and getting rid of hydrocarbons that might be sensed by the probe that OP has.

and

its doing a little fuel thing as well via the ECU where its getting some info also from the original style distributor.

but i mean a carbie car just does the rich thing on throttle lift off.
so ........its no worse than that?
or am i missing something.

i know here all the old school mechanics hated that lean thing that emissions cars did on throttle lift. thought it was worse for cars than the rich dump from carbies.
swings and roundabouts?

worst it can do is pop and bang through the exhaust when you come off the gas?
not exactly a backfire, more a detonation in the exhaust system.
bad for catylisers sure. but all this stuff was designed for preserving cats and cleaning up exhaust at the dirty times. idle and the big one, coming off the gas.

Posted by: wonkipop Mar 28 2022, 06:40 PM

ps

i was trying to look for info on the fpr in the factory manual.

i know its a sealed unit with the 1.8s.
no adjustment nut like a d-jet.

delivers normal standard fuel pressure.
and when the off throttle business happens manifold vacuum operates it and it opens and drops the fuel pressure in conjunction with the fuel cut off business the distributor sends signal to ECU for.

and really if the fpr is screwed on the L jet you throw them away.

but if they fail, ie the membrane its going to be dumping fuel via the vac line into the plenum. and thats going to be a lot of fuel i would think.
but there could be something in that. not sure.

Posted by: wonkipop Mar 28 2022, 08:11 PM

@http://www.914world.com/bbs2/index.php?showuser=25740 .

always have to go back and re-read this Ljet stuff carefully.

not sure if 1,8s incorporated the fuel shut off thing.
may not have been in all L jet systems, just for some cars.
someone like clay perrine would know.

1.8s definitely had spark cut off via the rotor for over rev.
whether that cut off fuel too i don't know, but i don't think so.
reason i say that is 75 calif 1.8s had a whole separate switch to cut off fuel to stop catyliser being ruined.
but as to coasting over-run, not certain. maybe note posted above inaccurate.

def adjust fuel pressure.
at low vac situations its 35 lbs.
and at high vac it reduces to 28 ilbs.
you test that as part of standard testing.

very definitely the throttle switch takes over at WOT.
just full on gives you fuel.
less clear about what tps does at idle (or throttle closed).
thinking about it, i believe its the AFM does it all.
when the throttle is closed the switch is simply sending a signal to the ECU that its closed. and ECU then knows this and does its routines based on other inputs.
i think only time ECU overrides the AFM is WOT and gives full enrichment.

so......
just not sure what could cause richness on over-run other than Van's suggestion that the distributor does the clean up via the timing. the fuel pressure lowers to assist due to high manifold pressure. and the ECU knows that the throttle is closed, but the engine revs (spinning) are high so it does an adjustment to the enrichment the AFM would usually signal at the flap position it is at because the decal valve being open (which is happening simultaneously with the fuel pressure regulator lowering fuel pressure).

Posted by: Brian Fuerbach Mar 28 2022, 10:34 PM

Tonight I measured the opening vacuum of the decel valve and it starts at 18 in-hg and is fully open at 20.

I also checked the wiring harness from the controller connection to the TPS (Pins #18 and #3 WOT). Idle checks out with "no connectivity", as soon as I crack the throttle I have a connection all the way to WOT. Not sure if it supposed to have continuous connectivity throughout the throttle range? The book I have says that idle uses #18 and #2 but "is no longer used". If this is not correct, let me know.

I tested the switch when it was off the throttle body not long ago and the contacts function properly but I thought there was some dead space in between idle and WOT?

Posted by: Van B Mar 28 2022, 10:55 PM

Your vac readings are what my decel valve yielded when my car was giving me high idle problems after deceleration. I turned the screw in until I got 20” and 23”.

Regardless, your numbers seem ok. Maybe it’s somewhat of a contributing cause, since we’re talking about a tuning issue and not a fault?


Throttle switch checks out. It doesn’t do anything between idle and WOT on an L-Jet. So, most importantly it does know that your throttle is closed. If it didn’t, I think you would have other issues.

Maybe that table I posted can help you improve your tune on the 123 distributor? Knowing vac levels for when the timing should retard or advance, and by how many additional degrees, as well as centrifugal data for the OE distributor would allow you to better mimic OE.

If that is all set up, I’d say the AFR you get is what it is and nothing to worry about.

Posted by: wonkipop Mar 29 2022, 12:51 AM

yes, that is how i read it. the ECU knows when the throttle is closed.
the rest of the time its hand off to AFM. but even at idle the flapper is moved.
? still it seems to want to know the throttle is closed.

although its not clear to me if it does another thing at full wide open.
or it just assumes if its not idle, then after that its open or on the way to wide open and lets the AFM do its job.

the test done by Brian says his throttle switch is fine.

part throttle decelerating might be another thing?
where you don't close the throttle off but only come down partly off revs rather than a hard release of the gas pedal. but just the same the flapper moves and electrons travel faster than air to the valve so the ECU is way in front of the O2 by the time it gets there, and its giving the right amount of fuel.

got to be all hard wired to the original expectations around the distributor and timing?

one thing i do know is those california EC-As in 74 just operated the distributor in retard mode only. so even when you were cruising they were forcing the engine to be retarded (slightly retarding the centrifigal position) and run "cleaner" on certain emissions. whereas the EC-Bs in 74 at least let you do advance at cruise and get fuel economy. and that was all just done off the distributor and pretty much nothing else. as far as i can figure out the california retard only distributor was a bit of blunt instrument that took a nice sophisticated instrument like a double can distributor and turned it against itself?

which might point to the 123 and just how the advance and retard work.

Posted by: wonkipop Mar 29 2022, 01:08 AM

i'll translate the above rambling thought.

because i have an 74 EC-B and so does Van B and Starbear, i'd be really curious to know what the AFR is after coming off the gas.

because those engines really only had to be non polluting at idle stationary.
that was the main test.
the federal emissions tests were different to the standards in california (CARB).
CARB was way stricter and became USA standard a year later.

so the idea of being rich as you come off the gas might not be out of line with the earliest version of the L jets.

i don't know for sure.

but the 74 EC-B engines were the only ones to make full use of the double can distributor.

the other three, the 74 california EC-A and the two versions in 75 don't. they leave the advance section of distributor un-used.

so maybe being a bit rich ain't all bad is what i am saying.

if it was a carb set up it wouldn't be bad necessarily.

but because you have a probe in your exhaust you almost know too much?

i only say this because i am almost sure (not 100%) that the way those original cars cleaned up hydrocarbons (unburnt fuel) was to do a late burn and also to burn it in the first sections of the hot exhaust. which would mean they would not show up at the end of the exhaust pipe where a probe might be detecting them. but they might have been still dumping fuel, just kind of crudely or bluntly dealing with it?

Posted by: wonkipop Mar 29 2022, 07:25 AM

i did a bit more reading.

because i was interested in the way that d jet has a fixed fuel pressure regulator but L jet has the vacuum adjusted regulator. i know the D jet injector is adjustable with the nut, but its a set and forget job. ie a static adjustment.

what L jet is doing is trying always to keep fuel pressure equal to manifold pressure in relative terms. when manifold pressure drops, (vacuum at idle or throttle close) it lowers the fuel pressure so that in relative terms it stays the same. injector delivers the same amount of fuel against the same relative pressure for certain time opening of injector.

there are more involved things it does too, which are to do with damping but thats beyond the simple principle. (and i got lost reading that).

i wonder if the fuel pressure regulator is not functioning properly when activated by vacuum. maybe an old stiff membrane? and fuel pressure is staying at 35 psi rather than dropping to 28 psi. i read they can fail in this way, not just by rupturing the membrane. back when the cars were newer it was rare for this kind of failure it seems.
but the cars are getting older.

i wonder if that could be doing anything as you come off throttle causing more fuel to dump in through injectors.

its just a thought.

you can do the test on the pressure regulator very easily to check the two values.
the procedure is in the factory manual.

Posted by: emerygt350 Mar 29 2022, 08:59 AM

That makes good sense.

Posted by: Brian Fuerbach Mar 29 2022, 02:37 PM

Appreciate all the replys. Took me a bit to read through and digest.

The car had a dual can distributor with both adv and retard connected. I hated the way it idled with the retard so I plugged it off, idled better. Finally changed to 123, best upgrade yet.

I will check the fuel pressure regulator to see if is functioning properly. The regulator looks like it has been replaced in the past as the cad plating looks nearly new.

At part throttle coasting the afr is not too rich, maybe high 10's -11. When I completely lift and coast it pegs full at 9. I live in the hills and if I use my gears to slow down the idle will be a little rough at the bottom but soon clears up. Was thinking it might be loading up a little bit. I started this topic because I had read that the AFR should go to 22 with the throttle closed during decel and mine did not, and partly because I am always looking for something to fix/improve on my 914.

Posted by: wonkipop Mar 29 2022, 03:02 PM

full test for the regulator is on previous page.
with car idling.
you pull off the vac hose to reg. should read 35 on a gauge.
put hose back on, should read 28. (all values approx or thereabouts).

both my fuel pressure regulators look beautiful and shiny cad plated.
both are at least 33 years old, suspect one is 48.
they did a nice job on plating them back in time.
(i have 2 because one is a visual emission cheat install for decel valve from back in the day).

topic is good, glad you started it.
i got into reading the patent documents for L jet.
and a technical explanation about how fuel despite being atomised by injectors coats surfaces of intakes rather than all hangs in air, but at another point in acceleration breaks free of surfaces. this causes two spikes and if it wasn't compensated for by the way L jet works the result would be a jolting rise in engine revs during acceleration. boy. i didn't fully understand it but i sure appreciated L jet a whole lot more. nothing to do with your issue, but i did at least stumble across the description of the why and how of the pressure regulator in L jet. which i had not understood properly at all.

i'll do some more searches when i get a spare moment and need a break from CAD.
see what i can turn up re rich on coasting. i'm interested to find out.

Posted by: Brian Fuerbach Mar 29 2022, 04:10 PM

Thanks for the input and appreciate you sharing your research. I come from years of tuning Weber and Dellorto carbs and now messing with L-jet. Will check the fuel pressure next.

Posted by: wonkipop Mar 29 2022, 04:45 PM

try measuring the Air Fuel Mix at idle too to compare to what you have on throttle lift and coasting.

the decel valve scenario is not unlike the AAV scenario at cold start?
sort of.

the throttle is at closed/idle switch position.
but during that AAV cold start scenario the AAV causes the flapper to open, causes the injector duration to increase and its part of how you get that quicker idle.
its got a scenario to over-write the warm idle scenario that involves more fuel.
there is other stuff going on too, like temp sensors.

at lift off coast its kind of similar but obviously different.
you have the decel valve in combo with the flapper over writing the throttle switch in closed position. its in combo with the fuel pressure drop.
the decel valve is letting the AFM draw air and move the flapper - it follows then it must also be getting a little fuel to burn on its way down to idle?
i mean thats what a decel valve does - at least in L jet?
but if i am correct its got no way of knowing how much fuel its giving other than by spec parameters around what fuel flows through the injector at the lower pressure. if the fuel pressure was higher its going to put more fuel in?
the injector opening is in a routine that conforms to amount of flapper movement, engine revs (from white wire on coil) and closed throttle position. its a timed opening?
so if fuel pressure is off then the timed opening of injectors will deliver too much or too little fuel.

i came across something that said min amount of pressure in system has to be 26 psi to open the injectors. don't know how accurate that is. but it does show that the injectors may have a narrow band of operation below 28 psi and that pressure drop takes them down to something close to the point where they won't open.

its just a thought. there will be L jet experts here that really know.
i am a bit like you. really trying to get my head around my L jet without giving myself too much of a migraine.

@http://www.914world.com/bbs2/index.php?showuser=25740 asked how does it know how fast the engine is spinning.
see here.
i like the way emery is curious about how the L jets are working.
the more stuff i read the more i came across explaining in historical terms just how hell bent bosch was on really simplifying the fuel injection system. anything they could do they did to not have an extra component in it.

Posted by: wonkipop Mar 29 2022, 05:04 PM

@http://www.914world.com/bbs2/index.php?showuser=760 Fuerbach
that description above about L jet really having no way to adjust for how much fuel its actually putting in provoked the next inprovement. closed loop systems with 02 sensors at the end of the track. at least then it could adjust itself on the fly and compensate for another part of the system that might be screwing up slightly.

thanks to your question i know that the harmless looking fuel pressure regulator is doing an important job with its vacuum section in the L jet cars. all the electronic injection german hokum pokem, then its got a cuckoo clock vacuum unit controlling half the hand cuffs on the amount of fuel coming out of the injector.

in a funny way you have given yourself a closed loop system?
you know too much about what its doing but there is no capacity to adjust itself on the fly.

i am sort of glad i don't know whats going on when i lift off the gas.
probably worse than yours.


what you said about getting to the bottom of the hills and having a rough idle -
sounds like its dumping a bit of gas in its not able to burn and fouling the plugs a bit?

Posted by: Brian Fuerbach Mar 29 2022, 07:36 PM

I am always looking for something to fix even if doesnt need it. I started using the wideband meter because I bought a rebuilt AFM from Fuel Injection Corp. and it was setup pig rich when initially delivered. The clock wheel was a half turn off. I have my AFR's pretty dialed now and all the other l-jet systems are functioning properly. I just wanted to get the decel afr's in line but sounds like that is just the way it operates.

This is what led me to think the TPS was malfunctioning. Just so I am clear, the only two pins used on the TPS are #18 and 3 which are input and WOT. The TPS switch is open between 18 and 3 at idle and closed just after tip in all the way to WOT. This is how mine is behaving.

Posted by: wonkipop Mar 29 2022, 08:26 PM

that is correct brian

Posted by: wonkipop Mar 29 2022, 08:38 PM

i am doing some more reading on just how the L jets handled backing off on decel.

i feel pretty sure that mine, without its decel valve connected would also be appearing to go very rich when i come off gas. doing a fuel dump more or less. probably like yours.
but maybe for slightly different reason. ie no decel valve.

there is no fuel cut off in these early L jets.

making sure the fuel pressure regulator is being operated by the vacuum line at both idle and coming off the gas is part of confirming the system.

but that i think is the way they are.

the distributor is definitely doing something to help clean up the hydrocarbons.
so it may well be that there is nothing here of concern if your afr etc are fine everywhere else.

by looking for info on your afr condition i now understand something about mine when its cold and i give it a rev and it almost dies and comes back to life. i'll post that up when i can summarise it simply and clearly. but its down to what the distributor is doing in that instance on my car.

Posted by: emerygt350 Mar 30 2022, 05:03 AM

The fouling is something to think about though. I have had many carbed cars over the years and decel fouling wasn't an issue. I think I have seen hints of it in my car but nothing terrible. When it warms up I might experiment with that. I can't imagine that was ignored by the manufacturer. Perhaps that is something we can tune away to some extent.

Posted by: wonkipop Mar 30 2022, 06:39 AM

know what you are saying.

i am curious about mine.

i don't have a probe in the exhaust to drive around and find out.
probably just as well.
but i guess when i get it in the workshop i can get an analyser on it and do some stationary tests watching what it does on the way down from closing the throttle from higher revs?

Posted by: emerygt350 Mar 30 2022, 06:47 AM

Man, trying to imagine my engine packed up with chickens. Don't post pre-coffee.

Anyway, fixed that.

I am going to try two things, one of which you could do if you have some hills around. I am getting a new probe (I think my 50 year old engine burns enough oil to do terrible things to o2 probes), and will look at both the numbers on the gauge but also plug condition. I have a hill that I know results in some fouling (not fowling, man that is something to imagine), and there is a parking lot at the bottom. I am going to let the engine drag down the hill (10% grade, maybe 500 feet decent, 1/2 mile) and then check the plug condition.

I found a 36 dollar wide band that should work with my autometer gauge, it will be interesting to see how it stands up to the original.
Dan

Posted by: Brian Fuerbach Mar 30 2022, 09:36 AM

While adjusting my decel valve I was able to simulate the same die and comeback to life situation as you. I think without the valve you will always have this issue.

Posted by: wonkipop Mar 30 2022, 04:09 PM

only does it to me when engine is cold and in warm up.
not been an issue for 30 years that i have to put up with in normal driving.
goes away once car is warm.

i've always thought, probably simplistically, it was that the afm flap bouncing back and briefly cutting the fuel. at the same time the distributor taken all the way to full retard (about 3-4 BTDC) snaps back off retard (engine almost stops and vac drops off) and goes back to 7.5 - which is the initial start firing position. after the two things happen and it all stabilises the car fires again and normal warm up resumes. lasts about 1 second in real time.

guess a decel valve while doing other things on deaccleration stops the afm flap closing so fast it travels past fuel cut off and then does the bounce back up, just as the engine catches again with the timing off retard.

why it does not do it warm, i have no explanation. perhaps it does but its recovery is so fast its not noticeable.

that afm flap going back to full rest position is about the only thing i believe that ever cuts fuel off. it does it in a real dumb way - just turns off the fuel pump.
but you would think it has enough fuel pressure to avoid scenario i outline above.
i dunno sometimes.

anyway i think confirm operation of fpr and knock it off the list.

lets us talk bs and read more stuff.

the only other thought i am having is that its pulling crankcase fumes at high vacuum after throttle closes because the pcv valve in the oil cap is not working. but we should leave that after fuel pressure drop on vacuum is ticked off.

i am sure some others will pipe in with that info in hand.

Posted by: wonkipop Mar 30 2022, 04:16 PM

whats the conversion rate from horsepower to chookpower?

Posted by: Brian Fuerbach Mar 30 2022, 05:10 PM

Chookpower you say?

Posted by: Brian Fuerbach Mar 30 2022, 05:20 PM

I believe that the decel valve has alot to do with your dipping return to idle. I could adjust the level of return to idle from "long hang time" to the "dip and stall" with a turn of the adjuster. When I finally got it where I wanted it checked out at the specified 20hg. Go figure. This is not to say that you would not be able to tune around it but the valve certainly serves a purpose.

Checking the fuel press tonight and maybe a little drive too.

Posted by: emerygt350 Mar 30 2022, 05:26 PM

Let's just blame autocorrect on all of that....

Really an interesting topic. I wonder if the afm shut off wasn't taking advantage of residual pressure. Sure the pump will stop when the afm closes but residual pressure will give another second of gas. If the engine is still running the afm will open again.

Just went for a little test run. Did the downhill drag (not intense, just normal kind of hill driving) and when I got to the bottom my idle was about 200 low. Engine was quite cool though. 186 head temps. It was hard to tell if I was fighting a computer induced rich condition rather than fouled plugs. The car ran fine beyond the low idle. By the time I got to the next stop sign and the temp came back up to 260ish, idle was back at 900.


I did notice that my vacuum on decel was 23. And that was not rpm dependent. If I was dragging down the hill at 4k rpms, the vacuum was the same as 1800 rpm.

In a 2.0 we have the mps measuring plenum vacuum for normal operating conditions (and at high vacuum fuel duration is cut) but we also have a more active tps, and one of its jobs is to tell the ecu to ignore the mps at closed throttle.

Need to get my new o2 sensor to play more with this... I just have to imagine that the engineers would have cut fuel almost completely during decel.

Posted by: emerygt350 Mar 30 2022, 05:30 PM

Perhaps it's a southern hemisphere thing...

Posted by: wonkipop Mar 30 2022, 05:39 PM

chookyard = chickenyard.

think the limeys call them chooks too.
a ye olde english thing more so than original aus slang.

limeys = usa slang. = poms in aus. translates as prisoners of his/her majesty i believe.
ie prisoners trapped in the motherland. ignoring as australians do that they were the original prisoners of another prison island. aus slang is endless circles of b s.

------

getting back to topic.
does this sound like your afr readings brian.

Posted by: wonkipop Mar 30 2022, 05:59 PM

yeah emery

what interested me was it does it cold but not when warm.
during warm up i believe the engine must be getting 2-3 times amount of enrichment.
and with vac working on fuel pressure regulator, fp goes down to 28.

and injectors won't squirt below 26. thats the bit i have to check. someone must know.
its not something i found in manual. it was just something someone wrote somewhere.

so maybe it can dip down enough when its cold to truly cut the injectors briefly.

because it don't happen warm.

as always. i dunno.

and i have read and read and read on the fuel cut off thing.
its not in this early version of L jet.
but i'm guessing that in a situation where the decel is disconnected and there is no action on the flapper that the throttle switch controls the fuel amount. so it delivers idle fuel portioning all the way down. ??? but not a cut off.

some slightly later bmws have the fuel cut off on decel. fuel is cut off at higher revs then as it drops to around 3000 revs fuel is resumed. but not it seems in these babies.

the decel does a couple of things.
it sort of simulates the way a carb can come down smoothly and resume idle.
ie it keeps combustion going and lets it subside gently to idle level.
but it also cleans up emissions because its letting in fuel on the way down via the flapper (i think?) and its burning it with air from the decel valve. and on top of that with an original distributor it retards timing back a little from centrifigal position and burns it slightly later - even past the exhaust valve and into upper stubs of exhaust manifold.
i think that is how they did it with these early L jets in relation to emissions.
all of which would lead you to a leaner condition measured with a probe. because its also burned up excess hydrocarbons in upper exhaust. these don't pop or detonate later in exhaust causing that usual burble - rather they get burned as they leave.
i think i have all that correct for a stock set up.

brians is a little harder to understand.

like how long is this rich thing persisting.
is it all the way down the hill/mountain coasting. or is it just initially on backing off to coast.

Posted by: wonkipop Mar 30 2022, 06:16 PM

here is another note on that decel thing.

the idea that the L jets can do a lean condition on deacceleration may not be entirely attributed to its primitive lunar module brain and pre program routines.
it might also be a kind of frankenstein sledgehammer/cuckoo clock attached to the side of it all with vac hoses.

ie it just burns the excess hydrocarbons on back off with a good old vac retard trick.

reason i say this is @http://www.914world.com/bbs2/index.php?showuser=8571 B brought up the different decel valve on the 75 1.8s on another thread.
and it is different. its a big monster flat can thing. which i know little about.

but i do know that the exhaust manifold stubs on the 75 1.8s were different as well.
they were thicker and held more heat in them. vw and porsche referred to these thicker stubs with real fancy words. "thermal reactors". not the thermal reactors we later came to know and love.

i'm putting 2 and 2 together here and coming up with 15 i know.

but a bigger decel can (more O2?), get those exhaust stubs nice and hot, change the distributor slightly (think its a different distributor too) and........do you burn even more hydrocarbons coming off the gas pedal and pass the emission test without an air pump.
and all the time you think the dumbo brain controlling it all is doing something smart with the air/fuel mix.

i dunno.

in 76 the 912E had to get an air pump. i don't know when and how the air pump kicks in. don't have a 912E. never seen one. none here. but they had L jet and had to get that air pump to pass the ever increasing emission test. 914 1.8s didn't need the air pump. so is the whole lean off thing about these gadgets and requirements of emissions.

i would have thought a temporary spike in richness on back off is not a terrible thing.
but if is persistent then that is something different i'm guessing.

Posted by: emerygt350 Mar 30 2022, 06:17 PM

I bet Mr. Injector could tell us exactly how they perform at sub 28 psi.

My gt350 has this crazy soft fall mechanism on the throttle body to stop the same kind of dip issue on throttle close. 14 years later, well 10 years after l-jet, with O2 sensors, and space shuttle computers, and they still couldn't keep a fuel injected motor running with a rapid throttle close. It was so bad, and fudged, that they wouldn't even give you fuel injection with a manual transmission. That took several years for cfi and a complete change to multiport injection (86) for the 302 ho.

Posted by: wonkipop Mar 30 2022, 06:34 PM

interesting what you say about no manual with fuel injection.

the EC-A, EC-B research i did turned up that VW pushed the L jet into production with primary focus on the VW 412 with auto trans. they could not make D jet work with auto trans and pass emissions test and be driveable. but they could achieve it with L jet.

3 months after the 412 comes the 914 with L jet. and a manual trans. and quite a different set up in terms of distributor, decel valve operation etc. all tweaked differently.

hard to find out info on 412 with the 74 L jet setup. and do i really want to know.
not really. but it is different the way it all works. think it even copped an EGR when the 914s didn't.

Posted by: Van B Mar 30 2022, 08:26 PM

That’s opposite. That example is going super lean.

Posted by: Brian Fuerbach Mar 30 2022, 08:40 PM

I checked the fuel press reg and all is golden.

I get the same low idle at the bottom of hills as you do GT350. Runs great as I get going again. I dont think it is fouling but maybe with the temporarily reduced head temps the computer is doing something to cause this. I will note my vacuum on the hill and see if it compares with yours.

Wonkipop, where in Oz do you live? I worked for a Brisbane company called EGR Automotive for a couple of years here in the US office. I currently have been employed for the last 13 years by an Aussie owned company.

Posted by: wonkipop Mar 30 2022, 09:06 PM

melbourne.

nihil44 who is on this site lives in brisbane. the weather there is nice (except in high summer when its horribly humid). i was originally born in far north queensland and my grandmother lived in brisbane where i spent teenage summers. lots of fun.
skateboarding, sailing, even some surfing if we could get out to stradbroke island.
its getting to be a big go ahead city these days. a giant urban agglomeration from brisbane to the gold coast.

good news about fuel pressure reg.

how long does the rich condition last on your probing spectrometer when it comes up.
is it all the way through deacceleration and on coasting all the way down hills?

Posted by: wonkipop Mar 30 2022, 09:38 PM

thats good,
its interesting for me then.
it seems to say with those 911s its not shutting off fuel, but the fuel is going to a lower level not influenced by air mass sensor (or equiv to afm, not sure what they have).
and since its not getting air its a pretty small amount of fuel?

must be what mine does when i back off gas without decel. just goes down to idle metering of fuel. i sure don't get what that pelican poster called popping. i might get some what i would call burble. so i doubt i get the rich thing fuel dump. probably get the opposite. not enough for anything much to happen except engine braking and a bit of fuel being expelled into exhaust and doing a little snap and crackle without the pop.
but there is no real combustion going on. its just spitting out a bit of fuel that is coming in. which is detonating in the exhaust. but its not a "real" rich condition thats occuring under true power combustion.

brian's thing is interesting.

is it possible that the oil filler cap might be coming into play.
given we discovered the horror of it being a pcv valve.

the mechanism seems to want to close off the crankcase if exposed to engine vacuum.

it can't get exposed to that when the throttle is closed. not via the throttle plate - crankcase vent port is above the throttle plate.
but could it be drawing as a result of the decel valve wanting to draw air in during decel. be exposed to fairly high manifold vacuum (draw) that way during over-run. is the pcv valve then meant to close in those instances. could it be drawing in excess of crankcase vapors, blow by fumes, oil mist etc.
could that increase the afr reading? "fowl plugs" as emery would say. you guys would know more than me about what can send one of those probes down the scale to say there was more "fuel" in it - besides perhaps real fuel so to speak.

Posted by: Brian Fuerbach Mar 31 2022, 02:02 PM

I was supposed to go the the EGR factory in Oz but missed out on the trip because my wife was 8 months pregnant at the time. I left the company shortly after.

Went to check vacuum on the hills and realized I couldn't. Thought it would be as simple as using the 123 dist app as it displays vacuum. Well, the app displays port vacuum not manifold vacuum. Going to look for my vac guage and try again.

I will also note the downhill afr's and rpms to see if they change at all.

The oil cap drawing fumes is an interesting hypothesis.

Posted by: wonkipop Mar 31 2022, 03:30 PM

a very long flight. still maybe one of the longest in the world.

going to aus is something you would probably do once and never again. too far?

but when you finally get there......

pluses
- language translates easily into amerilish without the use of a phrase book.
- friendly natives.
- better coffee
- beer
- good wine if thats your thing or the beer runs out.
- mount panorama

minuses
- smaller food servings.
- no rib joints.
- expensive fuel.
- bad drivers.
- dangerous wildlife.
- sharks.
- low ozone in atmosphere/uv levels that will age you 10 years in 2 minutes.
- too close to new zealand
- great ocean road ruined as drivers paradise.


had a look at EGR website.
realise i have used their building products.
namely waterproof internal boards.
i am not a fan of tiling. the boards are good stuff.
color range is better than the alternative manufacturers.
glad EGR survived the destruction of the domestic auto manufactures here.
one of the worst moves one of our former governments did.
decimated the component industry grouped around GM and Ford.

A visit to the factory would have put you in what i would call the inner ring of brisbane. would have been the edge of the city in the 50s. nicely positioned for further recreational after work activities. its a bit of a trip to get to the coast when you are in brisbane. it sits on moreton bay which is kind a tropical mangrove area. mud.
stradbroke island is the place to get to if you go there. car ferry ride. nice spot.
i rate brisbane as a serious city these days. rivals melbourne when it comes to food and coffee. melbourne is over-rated and has gone into decline. i've had some mighty fine meals in brisbane. used to do a bit of work up there and spend a bit of time in the town about 10 years ago.

Posted by: wonkipop Mar 31 2022, 04:30 PM

@http://www.914world.com/bbs2/index.php?showuser=760 Fuerbach

there was a discussion recently around the oil filler cap.
you might have already read it brian.

http://www.914world.com/bbs2/index.php?showtopic=358413&hl=nihil44++smoke+test

i attempted a cross section sketch of the cap and posted in that thread.

but this is probably a bit closer to what its really like.

Posted by: emerygt350 Mar 31 2022, 05:41 PM

Does that line head into the plenum or the air box?

Posted by: Brian Fuerbach Mar 31 2022, 08:08 PM

Wonkipop,
I did read the thread on on the cap. I came to the conclusion that the cap must function as a crankcase valve of some sort years ago while changing the seal and o-rings. I had tested my cap to see if the membrane was operational and it checked out.

emerygt350,
The crankcase vents into the rubber intake tube in between the Air box/AFM and throttle body. The AAR valve and Decel valves also enter in that area.

Posted by: wonkipop Mar 31 2022, 09:23 PM

emery, here is a photo of mine.
brian's will be the same.

i was having the thought because of the location where the decel hose connects.
its between the crankcase vent hose and the afm. it could sort of want to draw air from either direction.

but brian's report of the condition of his pcv valve/cap kind of puts paid to my theory.
so unless his cap is misbehaving since he tested it, its not a valid thought.



i did come across descriptions of momentary full rich as an afr reading.
happening immediately after closing the throttle.
if fuel has condensed on the inlet manifold and port areas.
closing the throttle and high vac moment causes condensed fuel to suddenly boil off the surfaces and be drawn into the combustion chamber and expelled. it doesn't last for long and is transitory.
depends a bit on the the design of the inlet system.

then there is always the question of the gauge and probe behaving correctly.
came across people describing some gauges actually measuring full lean, but having maxed out indicating this as full rich. ???? ie unreliable indications!

Posted by: emerygt350 Apr 1 2022, 06:42 AM

interesting. I assume that PCV system is like the 73 where it is vacuum sensitive. At high vacuum it actually closes up (well, it has a little metered breathing available), opening under low vacuum when you actually need it.


That initial rich is definitely a thing, but the going full lean on full rich is obvious on my autometer at least. The gauge actually kind of says "well, if we are going to be like that, screw you" and pegs itself to full lean and stays there for maybe a couple minutes. Mine is analog so there is normally movement in the arm at all times. When the computer gives you the finger, you can tell because it stops moving at full lean. It only does that when it gets too rich of a signal. Stupid. My digital AEM in the mustang doesn't do any sort of stupid thing like that.

Posted by: Brian Fuerbach Apr 1 2022, 01:26 PM

I have the wideband AEM Also.

Posted by: wonkipop Apr 1 2022, 04:33 PM

yes emery - am sure thats how it works on the 74 L jet too.
might also do a little balancing act between crankcase and inlet pressure differences at other times.

guess i was trying to think of the next thing to look at to be sure the info telling brian this was happening was 100% reliable.

is this a new thing brian? never done it before with the probe hooked up?

Posted by: Brian Fuerbach Apr 1 2022, 05:17 PM

The lower idle has always happened after a hill. Only noticed the correlation between afr and this after the probe was installed. Not sure where I read it but I was under the impression that fuel was to be cut off with the throttle closed. When this was proved wrong by the probe I wanted to find the issue. May not even be an issue. Maybe what I read about fuel cutoff was pertaining to D-jet?

Posted by: wonkipop Apr 1 2022, 06:11 PM

yes, its hard getting to the bottom of it all, once you start drilling down.

what i read says it is only very early D jet cars that have fuel cut off.
i try not to read anything on D jet. why go there? L jet serves as "amusement" enough with occasional migraine.

can't find anything definitive in the tech manuals about how ours behave exactly.
how does the ECU do it exactly. more gloss over descriptions. input this, input that and presto.

stuff i have read says do not cut the fuel off at all.
but they are meant to go lean.
back off and coasting were known as almost the dirtiest phase in an engine and the epa was out to mop it up.

so in the case of ours.
far as i understand it.
the distributor is sending the signals to the ECU and its sending them to the injectors to fire. twice for each combustion cycle. other inputs from the AFM and the temp sensors let the ECU decide how long for when it fires. the lowest setting it can get to is rock bottom. which would be the throttle switch on idle and possibly the AFM flap bouncing back further than the idle position it gets opened to when you have tuned it at idle. which likely explains the 1 second death my car gets cold when i rev it and it "dies" then resurrects all on its own. the decel is supposed to stop that retreat of the flapper right back to rest and below the position its opened to at idle. and it is open a little bit at idle.

to get extra fuel through those injectors on decel and coast, something would have to be telling it to keep the injectors open longer. it won't be the throttle switch because its telling the ecu the throttle is closed. and you have tested your TPS. it won't be the decel valve because its making the flapper behave exactly to the air demand its allowing. and you have tested and tuned your decel so its not that.

it won't be a temp sensor in the head because that would screw you up all over the shop.

it won't be the incoming air temp. same deal as cht.

it won't be the pcv valve. you got a good one.

if the probe is 100% right and info is good.
then the injectors are staying open too long and letting too much fuel in?
they will open and close by default regardless.
the degree of enrichment is by how long they stay open.

there is one other possibility.
which is a leaking cold start injector.
a lot of times you can tune around it and not notice it.

but in a situation like this where you have say tuned it at idle etc its dealing with it and you have tuned it out. but when it gets down to minimal fuel demand suddenly that bit of extra fuel is popping up.

the test for the cold start injector leaking is to pull it out.
get a bucket. get ready for a mess. go through the start sequence and crank.
watch it go off and finish its spray and the leave it sitting there and see if it drips.

PS - the californian 75 1.8s did have fuel cut off.
but i think that was for over-rev - this was in place of the speed limited rotor in the distributor. and that was to do with having cats.
the fuel cut off was a big switch that was mounted off the lower battery tray support.
kind of looked about the size of the normal efi relays we have mounted there.
but is not there on all the other 1.8s of 74 and 75.

Posted by: emerygt350 Apr 1 2022, 06:15 PM

No, no fuel cut on the djet, but I found the rich decel startling as well. I am used to the mustang which goes to 17 or so when you are dragging down a hill. The 84 cfi system is entirely different of course. Speed density with an O2 sensor.

Just really interested in why we don't see the lean mix on our cars (so far)
I want to figure out if this is just the way it is or if something isn't right. I need to look at the manual and see if they mention anything about coming down hills. I could imagine a decent hill could completely foul a plug if that is actually what is happening. I will check that this weekend.

Posted by: wonkipop Apr 1 2022, 06:21 PM

correct, not on yours emery.
but i think it did in 70 and maybe 71.
but i ain't argueing. L jets enough headache for me.
and if it did have fuel cut off would not have a clue how it worked.

Posted by: Van B Apr 1 2022, 06:39 PM

You guys just aren’t willing to talk about spark timing…
Riddle me this, why is timing retarded at idle conditions?

Posted by: wonkipop Apr 1 2022, 06:42 PM

i know the vac retard distributor did part of the work on the cleanup.
wasn't all down to the ECU being a transistorised german rocket scientist with the enrichment.

but when you look at it, the most extra retard its offering all the way down is about 3-4 degrees? i am pretty sure that is the extent of the retard.

in our double cans the vac advance comes off straight away the minute you close the throttle from cruise. its the other side of throttle plate. and the retard is the only bit still on. subject to manifold vacuum. so it immediately is pulling the distributor back the full retard. and it will be the full retard travel due to the strong vacuum. ie distributor is at centrifical advance - retard acting = actual advance. that was supposed to help clean up the gunk by burning it slightly later even as it came out the exhaust valve. the later burn meant less NOX in combustion and the hydrocarbons got done in a burn in the exhaust port after the valve and the upper exhaust. in the so called "thermal reactors".


the idea that brian had that the engine cools down coasting down hill does have merit. in the original set up the hydrocarbons that are there are being burned not entirely and not very well in the combustion chamber on back off.

they were going after NOX and could deal with it in the combustion chamber. get it lower. by making combustion cooler (later).
side effect. more hydrocarbons. burn those on the way out using heat of heads and upper exhaust and letting the combustion flame out into those areas. (side effect making that part of the heads hotter than normal) and further side effect - much more CO. ok they said we will put up with more CO because the cats are coming in a year or two and they turn the CO into "harmless" CO2 (and we don't know about ice caps melting yet so its ok) and H2O.

thats how i understand the emissions equipment to work.

the rocket scientist ECU helps heaps during normal cruise and acceleration etc. does it real good. but its still not genius enough to do the back off thing. and then all the semi mechanical, vacuum gizmos come into play. thing turns into a bavarian cuckoo clock at that moment?

so. maybe brian is on to something with the coasting down hill and cooling off.
like this is actually what they do.
when their so called "thermal reactor", afterburner idea gets cold enough to stop doing the burn.

and of course the EPA never tested that. just revved the engine on a test bed and measured the drop off and whatever came out the exhaust pipe.

one thing i did find out on the EC-A and EC-B research was how closely all these manufacturers tuned everything to the precise parameters of the EPA test to the letter. and then cheated like hell beyond that. thats how VW ended up getting caught in that first EPA cheat way back in 73.

has brian discovered something?

Posted by: wonkipop Apr 1 2022, 06:47 PM

i agree.
double vac can distributor is an integral part of the emissions equipment.

part of a sequence.

a sequence that produces more hydrocarbons in initial combustion.
then burns them up kind of crudely on the way out the door.

have i got that right Van.
you have your head around this better than me.

Posted by: Van B Apr 1 2022, 07:05 PM

Distributor vacuum is read/pulled from the throttle body not the manifold. So, that will be a different level of vacuum than in the actual manifold. And, the placement of the ports provides further difference.

Generally speaking, what the distributor sees at a closed throttle is no different at idle or any RPM when the throttle is closed.

Per the manual, there is a max of 32 degrees centrifugal advance and a max of 12 degrees vacuum advance. But, any time the throttle is closed the advance port is blocked, so that advance is immediately dropped AND retard is fully applied.

Thus, what remains is your centrifugal curve.
And again, per the manual, it would wind down from a max of 32 degrees at or above 3200RPM to 23.5-26.5 at or below 2500RPM, and finally 14.5-19 degrees between 1180 and 1500 RPM.
And since the throttle is closed, you would subtract the amount of applied retard to all of the above figures.

If the 123ignition distributor is not mimicking that profile then all bets are off for AFRs on closed throttle. The AFR is not measuring fuel nor air, it is only measuring effective combustion.

Posted by: Van B Apr 1 2022, 07:07 PM

Right now I have a relay board baking in the oven that I need to go check on lol!

Posted by: wonkipop Apr 1 2022, 07:24 PM

ok.
so i have the distributor bit right.
phew!

the afr measures oxygen to deduce effective combustion?

how does it do that - the effective combustion bit.
i've read a few things about 02 sensors but i don't quite get how they translate that into other information.

Posted by: Brian Fuerbach Apr 1 2022, 07:25 PM

I understood that the retard was mostly for idle emissions. When I had mine hooked up the engine would get hotter if left idling. Never could get a consistent idle either. I have heard many say that it is required for the proper idle with L-jet but I tried and hated the tune.

Posted by: Van B Apr 1 2022, 07:32 PM

Charts like this are worth so much IMO.


Attached thumbnail(s)

Posted by: wonkipop Apr 1 2022, 07:38 PM

no, not just idle if you happened to own a 74 cal 1.8 or any of the 75s. they were just vac retard connected. which meant the ignition was retarded any time you were in a manifold vac situation with the engine. ie cruise. or throttle shut down.

only the 74 1.8 49 state car had the advance hose actually hooked up to the t/b to give you a big vac advance at cruise/light load. mostly for economy and cool running.
but as soon as you closed the throttle the same scenario would go into play as per all the others with regard to distributor.

see van's masterful economical description.

the californians were using that retard to clean up emissions at cruise in 74.
and the rest of the USA was doing the same thing in 75.
with added EGR in california which did some stuff emery is right up on.


and yes brian it really does make them idle noticeably hotter.
spot on there.
so much so that i tend to avoid driving mine in high summer in australia where air temps get up easily into low 40C range.

Posted by: Van B Apr 1 2022, 07:44 PM

In simple terms, ionic transfusion creates a voltage charge that is measured by the sensor. An O2 sensor pulls outside air into the sensor. The less dense oxygen in the exhaust pulls ions across a medium and creates a resulting current. But in actuality, the less oxygen, the less ions are pulled, meaning a lower voltage is measured. So the richer the mixture, the higher the volts.

Clear as mud?

Posted by: wonkipop Apr 1 2022, 07:44 PM

thanks for that chart. i am going to study it now and make myself get this.

Posted by: wonkipop Apr 1 2022, 07:47 PM

i'll see if i can get my head around it.
i like trying to at least half understand how a thing really works.

Posted by: wonkipop Apr 1 2022, 07:51 PM

your 914 is lucky its got you as an owner.

Posted by: wonkipop Apr 1 2022, 08:16 PM

that chart was great.
just as a translation device.

(still ploughing through the scientific mud )

dug out my old illinois emission test of 1990.
here is how it stacked up? - back then when it was still a teenager and the nice lady stuck a hose up its posterior.






high idle.
HC ppm 0128
CO% 4.20
CO + CO2 % 15.31

low idle
HC ppm 0635
CO% 01.88
CO + CO% 11.17

i was always interested in the stated limits of CO + CO2 % whenever i looked the test.
because it exceeded both. both were stated as limit of 6.00
but now the penny finally drops. i'm slow. it had to be over that figure? not under?
and under on all the others. HC CO.
you got to remember i am an aussie. no smog tests here.
no real emissions gear until the 80s.

hidden in details. tacho reading for high idle 2703.
no tacho reading recorded on test for low idle.

Posted by: Brian Fuerbach Apr 2 2022, 02:42 PM

How do these chart values translate to afr on my guage? Or do they?

Is 11.7 at low idle same as our gauge reading?

Posted by: Van B Apr 2 2022, 03:45 PM

Yes. AFR is the bottom scale. There are various gases that can be measured and then calculated to assess AFR. This chart overlays CO, CO2,H2, and O2 as percentage because in olden times you could only measure the gas directly and then you would use the chart to calculate the equivalent AFR.

Now you have a little gauge that does it for you

Posted by: wonkipop Apr 2 2022, 06:19 PM

@http://www.914world.com/bbs2/index.php?showuser=760 Fuerbach

although that specific chart has the disclaimer "based on a specific fuel formula".

i'm guessing its pretty close for most petrol fuels?
Van B can do a bit more educatin'.

brian are you asking is what is the oxygen line left of the stoichiometric value?

here is where i get corrected by Van - hopefully.
after reading up on your tip on the clear as mud science of the probe/sensor.
when in rich territory the O2 sensor at that point is measuring unburned fuel?
not oxygen? its detecting the amount of unburned fuel via that electrical thing it does.
either side of the ideal point its flipping one way or the other?

there isn't an unburned fuel line on that graph.
but there was in my emission tests in 1990. hydrocarbons at ppm.

Posted by: emerygt350 Apr 2 2022, 07:54 PM

I am not entirely sure the retard was just for emissions. I suspect it was also for a nice idle. It basically creates a second curve for the distributor. You can start the car nice and easy with no throttle input and as soon as you start to accelerate the timing jumps to a point where your idle would have been obnoxiously high at closed throttle. Advanced ignition with extra air at start isn't the best start scenario. It works but it isn't exactly refined.

Posted by: Van B Apr 2 2022, 08:00 PM

But there is unburnt fuel on that graph. That’s what each of those gases are, combustion byproducts from burning hydrocarbons in air. I have no understanding of the chemistry, but I can see that stoichiometric combustion maximizes CO2 and minimizes other gases.

So, when you’re rich, there’s not enough air to burn all the added fuel. What results is incomplete combustion and a not so hot flame. When you’re lean, there’s not enough fuel to consume all the air. What results there is most likely detonation. That’s why O2 climbs in both Directions away from stoichiometric.

Fuel air mix is kinda like setting an oxy-acetylene torch. But with one massive difference, a moving engine. Compression and the act of compression heats the fuel air mixture, and the faster the piston moves, the more aggressively it’s heated. So, the spark can ignite the mixture sooner… further and further before TDC aka maximum compression.

The case I’m making here is that when you ignite the mix matters just as much as the mix you ignite.

Brian says he has an 11.7 AFR at idle, which is decently rich. But can you see how much more rich your AFR would read if you advanced the spark timing even further?

Now that I know what his AFR at idle, I think the AFM needs to be leaned out AND the spark advance curve corrected. Just some regular tuning… but I still think Brian should start with getting the aftermarket distributor to work like OE as much as possible for all round performance and drivability.

Posted by: wonkipop Apr 2 2022, 08:15 PM

i think in the case of the L jets it was for emissions.
makes them run hotter than ideal at idle.
so its not the best point for idle.
and they are known for it.

you are correct with all the rest of it.
starts easily at the ideal point. no vac. no retard. then goes to retard.
and yes snaps straight off when you open the throttle so you get the ideal advance curve of the cent. dist operation.

its a kind of exaggeration of the scenario you describe.
they just go for more retard than is "ideal". or its "ideal" when it comes to NOX.
its NOX they were going after. main ingredient of photo chemical smog.
so yep, makes it easier to start.
snaps off for good response when you put the boot in.
but you are coming from even further back on the back foot.

Posted by: wonkipop Apr 2 2022, 09:06 PM

digesting.

Posted by: Brian Fuerbach Apr 3 2022, 12:12 AM

Let me clarify, my engine does not idle at 11.7 I was asking if the 11.7 on the chart correlated with afr on my gauge readings. My engine idles at 13.5 but idles better when richer. Any leaner makes for a rough idle.

The curve I programmed into the 123 was a copy of the proper factory curve with advance but no retard.

Posted by: wonkipop Apr 3 2022, 01:18 AM

Posted by: wonkipop Apr 3 2022, 01:28 AM

i know that chart co-relation i did was a bit rough.
because i just equated CO levels to what i had measured back in 90.
i was just fooling around.
but i was in about the same vicinity as you at idle?

if i used CO2 on the same chart (easy to get off my emission test back then - just subtract CO from the CO + CO2 percentages) it doesn't co-relate to the same AFR i get off the chart as the CO. its a little different. but it is still in that vicinity.
by 11.7 do you mean the 11.17 i quoted from my emission test of 1990for idle CO + CO2? in which case I can find both curves or lines. i have the CO - which was 1.88% (gee i was .12% under the factory manual, not good) and i had the CO +C02% as 11.17%, so i could derive a CO2 % if i wanted to of 11,17 - 1.88 = 9.29%. and then i could go on to Van's graph and look at 9.29% CO2 line and see where that landed me on AFR. which would be 12.0 and under. 11.7? thats richish. thats what i mean. but i'm not sure how you can go directly from those measures i had in 1990 to the graph that Van posted. thats for a certain type of fuel. i was just doing a ball park thing.

they did apparently set them up a little richer as air cooled engines.

geez, i don't know if i want to go into this O2 territory with mine and probes!
but i am counting on Van to make the mud settle to the bottom of the pond for me.
.....i am an old bastard. trying to keep up. waste of time?

i'll leave Van to comment on not incorporating retard.
but its going to have an effect.
i think what it means is once it comes off vacuum our mechanical advance is like yours.
but on the way back down its different in terms of timing.

and then we have vac advance. whole other thing?
but thats just at cruise? i believe. not when your foot is mashed. its all mechinical again when your exercising your right foot downwards.

Posted by: Van B Apr 3 2022, 08:09 AM

Brian, good to know. To be clear, I don’t have high confidence on how great AFRs would be on a prolonged decel. My interest in this topic is because as a mediocre superbike racer many years ago, I learned the value of a good off-on throttle transition.

What we would tune for was a little richer on decel for added cylinder cooling, but not so much that it would load up/bog at the first touch of the throttle. You also didn’t want it so lean that temps were high and you would get that detonation pop as soon as you dumped more fuel and air in.

I’m getting off topic here, it what I’m driving at is, without knowing what other L-Jets work like or what the factory intended, I can only assume that the engine should run mildly rich on a closed throttle decel.

And, I’m not sure if retarding the timing on closed throttle will get you all the way there, but it will get you closer.

@http://www.914world.com/bbs2/index.php?showuser=24231 for your educational purposes question. Retarding the timing means the spark is delivered closer to TDC, but always before TDC. To paint two ends of the spectrum, if your engine is running 5000RPM at WOT, you are sucking in all the air possible, the fuel injectors are working at full steam to add a matching amount of fuel, and the pistons are smashing that mixture into a hot cylinder as aggressively as it can. In this scenario you need to advance the spark considerably so that you can ignite the mix at the right time to get a smooth even combustion burn.

Conversely, if you are closed throttle at 5000RPM, there is very little air coming in, and accordingly, much less fuel. So, there is less to compress, which means less heating of the fuel air mix from compression. But there is still a very high piston speed to account for. So, you ignite that closed throttle mix sooner than at idle but not as soon as you would a WOT mix of the same RPM.

Posted by: wonkipop Apr 3 2022, 03:41 PM

ok, now i see what you are driving at. i was down there at idle. but now i am up with you at high speed back off, but a f r is down at idle level. got you.

and of course that is what our standard distributors do.
immediately offer that retarding of the pure mechanical position.
to an ideal spot for that.

so i was understanding you. i was just somehow stuck on your advancing at idle analogy. but i get it now what you were saying.

have you ever been able to determine what the vac retard amount is in the literature.
it would be maximum retard at higher revs back off too in mine. no decel valve.
different with the decel valve as its breaking the vacuum and reducing it.
assuming that is at idle that the vac level isn't enough to fully move the retard position and only goes a part of the way of its travel.

Posted by: Van B Apr 3 2022, 04:12 PM

Nothing in the manual but you can measure it with a timing light at idle I bet.

Posted by: wonkipop Apr 3 2022, 04:23 PM

the easiest way to know that it is for emissions in L jet is the tune up procedure emery. time it with the hoses off the distributor and plugged. get it sweet.
then plug them back on. and do a final tweak of idle speed.

kind of tells you that you then turn yourself over to faith in the vac system of the distributor doing a distortion of that best state of tune according to its own devices.
with the pure intent of altering the NOX and HC popping out the tail pipe.

i can get it slowly bit by bit as i go along now after studying this graph.
part of what VW were doing was idle tuning/timing with the hoses off somewhere near where the NOX line and the CO line cross. the HC is also nearby as a minimumish level.



as to the precise chemistry of what then happens if you "artificially" shift that best state of tune with a vacuum induced retard i need to know more than perhaps i care to.
Van is more eloquent.
the result is even lower NOX than you would get at the tune with the hoses off and HC still gets burned, but less in combustion moment and remainder in the upper reaches of exhaust system and exhaust port of head. which is where the engine temp goes up. in those areas. hence the engine running hot at idle characteristic. the EPA was fixated on NOX to begin with. along with hydrocarbons.

Posted by: emerygt350 Apr 3 2022, 05:06 PM

I am coming to this system from ford's CFI system and that one is 10 years later and far more computer (hah) intensive, as well as epa strangled. Ford actually used the timing to set the idle on my mustang. If you check your timing at idle on an 84 cfi 302 HO it will often read 20 or so degrees advanced and 14.7 on the afr. Since then I have been very interested in idle stability and quality and timing. I have found, even on the 914 djet, that it is expecting a very specific timing for idle to work well. On my 914 it is 9 degrees advance. I checked it yesterday and 9 degrees at idle and 33-34ish all in is where it is at (assuming my light is any good and my marks are ok). It was around 29 at 3200. When I move off of that the idle gets unpredictable, not pleasant, and sometimes stinky. When I had the original dizzy on there with advance and retard, it was a real difficult time getting everything to play right but I suspect that was mostly the bad triggers.

Posted by: Van B Apr 3 2022, 05:41 PM

I've learned that adaptive dwell is like a cheat code for your distributor.
Seriously, I am so f'n pleased with the hall effect setup of my pertronix

Posted by: emerygt350 Apr 3 2022, 06:13 PM

Yeah, Ford guys complain but the tfi hall effect dizzy is quite an improvement.

Odd thing is that most mechanics screw up timing a cfi mustang because they don't unplug a little wire from the tfi module that tells the computer to advance the timing at idle. If you do it right on that car it is supposed to be 8 degrees adv with the wire unplugged. Most of us push it to 9 or 10. I completely forgot about that (my mustang hasn't needed my help in several years). Interesting that the base timing on those would be 8-10 but then the computer takes over, Jacks the timing way up, and probably does some magic with the afr and you end up at 850 rpm in neutral.

If anything, mucking with these early systems is really making me appreciate both the early engineering and the later engineering. My 84 gt350 is the last year before the dreaded "engine light".

Posted by: wonkipop Apr 4 2022, 03:56 AM

i inspected our 80s vintage gizmo analyser, tuner with a screen etc the size of a doctor who dalek that sits in the corner.

the screen bit is kaput, needs some vintage expert to fix that bit up.
some kind of oscilliscipe sci fi thing.
but the exhaust gas analyzer bit still works.
does 4 types of gases and ingredients.

CO

CO2

HC

i think it does NOx, i think that is what mike said.

has no scope for oxygen because thats something you breathe?
and bosch were holding the patent for those probes close to their chest even in the 80s.

i'm going to fire it up on the next tune up.
going old school. i'm an old man so its legit.
be catching up on technology just using the machine?
i used to static time my square back with a light bulb. (quick duck a peradactyle is swooping us).
onward into the space age after its already gone.

Posted by: emerygt350 Apr 8 2022, 06:07 AM

Finally got my new O2 sensor. On decel mine is running between 12 and 13. More towards 13 most of the time. Looks like it's kind of binary so I think something specific is occurring (mps/decel combo) and it is steady across the decel. So definitely not full rich.

Posted by: Van B Apr 8 2022, 07:23 AM

you're definitely in a good spot.
I know we're talking about D-jet vs L-jet here, but you and Brian have the same distributor. Do you know what your advance is in a closed throttle/decel situation?

Posted by: emerygt350 Apr 8 2022, 11:02 AM

It would be entirely dependent on the motor rpm and the curve built into the 123, the vacuum advance is hooked up correctly so on decel there will be no vacuum there. I have the potted version so I can't check my advance through blue tooth.