L-Jet going full Rich on Deceleration Options

[wonkipop]

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.

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?

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?

yes, its hard getting to the bottom of it all, once you start drilling down.(IMG:style_emoticons/default/laugh.gif)

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.

[emerygt350]

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.

[wonkipop]

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.

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

[Van B]

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

[wonkipop]

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.

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".
(IMG:style_emoticons/default/laugh.gif) (IMG:style_emoticons/default/laugh.gif)

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?

[wonkipop]

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

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.

[Van B]

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.

[Van B]

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

[wonkipop]

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.

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.

[Brian Fuerbach]

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

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.

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.

[Van B]

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.

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.

Charts like this are worth so much IMO.

[wonkipop]

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

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.

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.

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.

[Van B]

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.

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?

[wonkipop]

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.

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.

Charts like this are worth so much IMO.

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

[wonkipop]

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.

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?

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

[wonkipop]

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

your 914 is lucky its got you as an owner.

[wonkipop]

that chart was great.
just as a translation device.

(still ploughing through the scientific mud (IMG:style_emoticons/default/beer.gif) (IMG:style_emoticons/default/laugh.gif) )

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.

[Brian Fuerbach]

that chart was great.
just as a translation device.

(still ploughing through the scientific mud (IMG:style_emoticons/default/beer.gif) (IMG:style_emoticons/default/laugh.gif) )

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.

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?

[Van B]

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 (IMG:style_emoticons/default/shades.gif)

[wonkipop]

@Brian 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.