L-Jet going full Rich on Deceleration Options

[wonkipop]

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?

[wonkipop]

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.

[emerygt350]

That makes good sense.

[Brian Fuerbach]

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.

[wonkipop]

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.

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. (IMG:style_emoticons/default/blink.gif)
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. (IMG:style_emoticons/default/sad.gif) (IMG:style_emoticons/default/smile.gif) 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. (IMG:style_emoticons/default/beerchug.gif) i'm interested to find out.

[Brian Fuerbach]

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.

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. (IMG:style_emoticons/default/blink.gif)
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. (IMG:style_emoticons/default/sad.gif) (IMG:style_emoticons/default/smile.gif) 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. (IMG:style_emoticons/default/beerchug.gif) i'm interested to find out.

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. (IMG:style_emoticons/default/beerchug.gif)

[wonkipop]

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.

@Emerygt350 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.

[wonkipop]

@Brian 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. (IMG:style_emoticons/default/smile.gif)
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?

[Brian Fuerbach]

@Brian 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. (IMG:style_emoticons/default/smile.gif)
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?

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.

[wonkipop]

that is correct brian

[wonkipop]

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.

[emerygt350]

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.

[wonkipop]

The fowling is something to think about though. I have had many carbed cats over the years and decel fowling 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.

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?

[emerygt350]

The fowling is something to think about though. I have had many carbed cats over the years and decel fowling 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.

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?

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

[Brian Fuerbach]

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.

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.

[wonkipop]

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.

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.

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.


(IMG:style_emoticons/default/beerchug.gif)

[wonkipop]

The fowling is something to think about though. I have had many carbed cats over the years and decel fowling 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.

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?

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

whats the conversion rate from horsepower to chookpower?

[Brian Fuerbach]

The fowling is something to think about though. I have had many carbed cats over the years and decel fowling 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.

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?

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

whats the conversion rate from horsepower to chookpower?

Chookpower you say?

[Brian Fuerbach]

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.

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.

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.


(IMG:style_emoticons/default/beerchug.gif)

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.

[emerygt350]

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.