L-Jet going full Rich on Deceleration Options

[emerygt350]

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?

[Van B]

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?

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 @Brian Fuerbach 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.

[emerygt350]

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?

[Brian Fuerbach]

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.

[emerygt350]

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.

[wonkipop]

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...

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.

[r_towle]

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

[wonkipop]

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.

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.

[emerygt350]

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.

[wonkipop]

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.

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.

[emerygt350]

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?

[wonkipop]

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?

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.

[emerygt350]

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

[Van B]

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.

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

74 model would be using 205 AA

[wonkipop]

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

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.

[wonkipop]

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.

[wonkipop]

@Emerygt350 .

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).

[Brian Fuerbach]

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

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?

[Van B]

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.

[wonkipop]

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.

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.