‘74 1.8L L-Jetronic Cold Start Low Idle, Mystery solved! Options

[wonkipop]

It's been ages, so you might have done this already, but have you put a vacuum gauge on it?

Have you verified you are at the correct timing? Again check that the distributor is working correctly. Don't fear the distributor, super easy to pull out and clean/lubricate.

Yup. There’s only one mark on this engine. Done it three times now as one was the experiment to mimic the California setup… didn’t work. I’ve also confirmed that I get 30 degrees of advance at 3k RPM.
I’m not pulling it because it’s operating as it’s supposed to. But also, I would prefer to have someone who can show me how all the bits work as opposed to blind exploration.

I will put a vacuum gauge on both ports this weekend just to confirm there are no leaks.

that distributor sounds to me to be working just fine if its pulling that much advance.
at least on the advance side.

[Van B]

Thanks @wonkipop
I found this guy on the inter webs:
https://www.summitracing.com/parts/smp-ac358
It looks like a cost effective clone and is just about right on price when measured against the ass pain of fully tearing mine apart.

Also, as I stated a while back, I’ve already moved the nut to the outside of its adjustment… no change.

I’ll chew through that material this weekend.

[Van B]

Also, can anyone tell me why the dual relay has a plug on one side and a bird’s nest on the other?

[Van B]

It's been ages, so you might have done this already, but have you put a vacuum gauge on it?

Have you verified you are at the correct timing? Again check that the distributor is working correctly. Don't fear the distributor, super easy to pull out and clean/lubricate.

Yup. There’s only one mark on this engine. Done it three times now as one was the experiment to mimic the California setup… didn’t work. I’ve also confirmed that I get 30 degrees of advance at 3k RPM.
I’m not pulling it because it’s operating as it’s supposed to. But also, I would prefer to have someone who can show me how all the bits work as opposed to blind exploration.

I will put a vacuum gauge on both ports this weekend just to confirm there are no leaks.

that distributor sounds to me to be working just fine if its pulling that much advance.
at least on the advance side.

The retard also works, obviously since idle climbs when I disconnect the line.

[wonkipop]

Thanks @wonkipop
I found this guy on the inter webs:
https://www.summitracing.com/parts/smp-ac358
It looks like a cost effective clone and is just about right on price when measured against the ass pain of fully tearing mine apart.

Also, as I stated a while back, I’ve already moved the nut to the outside of its adjustment… no change.

I’ll chew through that material this weekend.

gold.
might just have to get one of those myself.

[wonkipop]

got the same plastic relay.
(think these are replacements for originals which had metal casing?
this one has been in mine since i got it, that was 1989).

plug one side.
wiring other.

[wonkipop]

an original type relay.
same "rats nest".

battery acid got em?
or just plain water. sit right under dopey bit of open grill without a raintray that the porsche stylists never quite resolved?





from the EFI manual.
same rats nest.
not a relay i have dug into. or had to yet.
plug and rats nest is standard kit.

[emerygt350]

I meant how much vacuum the engine is pulling.


I also wonder about when that retard is supposed to stop. Is the AAR enough of a leak to cause the retard to stop retarding the timing? I kind of doubt it but it is possible. If so that would be a double whammy on a cold start. Retarded timing and not enough fuel and air.

[wonkipop]

It's been ages, so you might have done this already, but have you put a vacuum gauge on it?

Have you verified you are at the correct timing? Again check that the distributor is working correctly. Don't fear the distributor, super easy to pull out and clean/lubricate.

Yup. There’s only one mark on this engine. Done it three times now as one was the experiment to mimic the California setup… didn’t work. I’ve also confirmed that I get 30 degrees of advance at 3k RPM.
I’m not pulling it because it’s operating as it’s supposed to. But also, I would prefer to have someone who can show me how all the bits work as opposed to blind exploration.

I will put a vacuum gauge on both ports this weekend just to confirm there are no leaks.

those distributors are unobtainium.
i also would only fully disassemble under strict observation by my mechanic.
actually i would probably just hand it across to him given that its just not replaceable.
but mine works fine and has been lubricated etc.
i'd say yours is the same.

to think a lot of these got thrown away years ago in carb conversions. (IMG:style_emoticons/default/sad.gif)

[emerygt350]

I found that my trigger points and bearings were all a little suspect so I put it on the shelf and installed a 123ignition distributor a few weeks ago. Quite an improvement and no more wear and tear on my old 009 dizzy.

[wonkipop]

I meant how much vacuum the engine is pulling.


I also wonder about when that retard is supposed to stop. Is the AAR enough of a leak to cause the retard to stop retarding the timing? I kind of doubt it but it is possible. If so that would be a double whammy on a cold start. Retarded timing and not enough fuel and air.

if that was the case it would just make it idle better (but pollute more).

these things start on 7.5 BTDC. fire on that and then immediately (almost) the retard sucks it back to around 4.

the retarded timing is what makes the warm up idle harder to achieve.
i'd say the difficulty with the cold idle van is having is a sign the distributor is wide awake, young at heart and raring to do its job holding the engine back when its trying to wake up and take some deep breaths.

the retard never stops while the engine is at idle.
its always retarded. it starts at 7.5 which is "pre-idle" but that is the only bit that is "unretarded" so to speak. i doubt it would fire at 4, or it would have a hard time firing.

[emerygt350]

I meant how much vacuum the engine is pulling.


I also wonder about when that retard is supposed to stop. Is the AAR enough of a leak to cause the retard to stop retarding the timing? I kind of doubt it but it is possible. If so that would be a double whammy on a cold start. Retarded timing and not enough fuel and air.

if that was the case it would just make it idle better (but pollute more).

these things start on 7.5 BTDC. fire on that and then immediately (almost) the retard sucks it back to around 4.

the retarded timing is what makes the warm up idle harder to achieve.
i'd say the difficulty with the cold idle van is having is a sign the distributor is wide awake, young at heart and raring to do its job holding the engine back when its trying to wake up and take some deep breaths.

the retard never stops while the engine is at idle.
its always retarded. it starts at 7.5 which is idle but that is the only bit that is "unretarded" so to speak. i doubt it would fire at 4, or it would have a hard time firing.

Yes, that is my point. If it was designed to allow enough air to stop the retard then this problem gets worse since you are working against both issues. No clue if that is the case though. I will pull the retard line on mine tomorrow when it is in full Aar and see if there is vacuum at the port or if the idle increases more with it disconnected and plugged. Just out of curiosity.

[wonkipop]

I meant how much vacuum the engine is pulling.


I also wonder about when that retard is supposed to stop. Is the AAR enough of a leak to cause the retard to stop retarding the timing? I kind of doubt it but it is possible. If so that would be a double whammy on a cold start. Retarded timing and not enough fuel and air.

if that was the case it would just make it idle better (but pollute more).

these things start on 7.5 BTDC. fire on that and then immediately (almost) the retard sucks it back to around 4.

the retarded timing is what makes the warm up idle harder to achieve.
i'd say the difficulty with the cold idle van is having is a sign the distributor is wide awake, young at heart and raring to do its job holding the engine back when its trying to wake up and take some deep breaths.

the retard never stops while the engine is at idle.
its always retarded. it starts at 7.5 which is idle but that is the only bit that is "unretarded" so to speak. i doubt it would fire at 4, or it would have a hard time firing.

Yes, that is my point. If it was designed to allow enough air to stop the retard then this problem gets worse since you are working against both issues. No clue if that is the case though. I will pull the retard line on mine tomorrow when it is in full Aar and see if there is vacuum at the port or if the idle increases more with it disconnected and plugged. Just out of curiosity.

ah yes. i see what you are saying.

however at the amount of simulated throttle opening the AAV does i doubt the manifold alters from being at vacuum. which would have to be the case for it to come off pulling the retard side of distributor.

let us know how your test goes.

i tend to think the above scenario would still be a case of improving idle, not making it worse. its would let the engine idle at 7.5 btdc with a part cracked open throttle.
which is better than 4? i mean that extra retarding of the timing by the retard can is an emission mechanism, not to assist with cold start. or do i have that wrong?

[Van B]

Yeah so, little to no vacuum while cranking, then on kick over, engine vacuum pulls the retard.

Not sure what this means, but if I pull the oil cap with the car running, it instantly dies. So vacuum abounds I suppose.

F**k it, I’ll vacuum test everything I can get the mighty vac on this weekend lol

[Van B]

I found that my trigger points and bearings were all a little suspect so I put it on the shelf and installed a 123ignition distributor a few weeks ago. Quite an improvement and no more wear and tear on my old 009 dizzy.

I see a 123ignition in my future, but not until I’m satisfied with the present state of tune.

[wonkipop]

Yeah so, little to no vacuum while cranking, then on kick over, engine vacuum pulls the retard.

Not sure what this means, but if I pull the oil cap with the car running, it instantly dies. So vacuum abounds I suppose.

F**k it, I’ll vacuum test everything I can get the mighty vac on this weekend lol

its all sealed.

another area you can get problems from in L jet is the valve cover gaskets.
but you would know if that was an issue. there would be oil leaks.
but the L jet does need to be buttoned up tight.

how are the gaskets in the oil cap. in good condition?

the AFM can't measure an air leak as big as the oil cap off which is leaking air straight into the hose from the AFM to the TB.

i guess the valve covers mean it can leak air via the crank case up into the PCV and from there into the same hose.

doesn't like false air from anywhere that the AFM can't measure.

i had a leaky throttle body gasket that seemed to kick in when the engine got hot.
thermal expansion. started fine. drove ok for 10 minutes, then went haywire.
i could keep it running but it would die at the lights. replaced the TB gasket with a new one from 914 rubber. problem went away. the old gasket had just gone hard.
surprised me how it managed to leak.

[Van B]

I got oil leaks from everywhere. Most are just weeping but the RMS and what I think is the Speedo gear are the worst.

[wonkipop]

i think i got my head around what emory is getting at.

he is saying that AAV is sufficiently strong to stop full retard of dist at warm up.
ie - when cold the distributor doesn't retard.
but your distributor might be sticking at retard. not moving.

an interesting idea.
not sure if that is so. that AAV would be sufficient to neutralise the vacuum retard and then as it closes the retard comes up to full strength and fully retards. but of course how would distributor go to full retard (to stick there) in the first place if the AAV is already open.

still - had not thought of it that way.

[wonkipop]

this is where my thinking is at Van.

and i will reduce it to as simple as i can get it.

the L jet in these is a primitive open loop system.

the ECU can respond to mixture enrichment from the two temp sensors.
1 telling it the temp of incoming air.
11 telling it the temp of the engine.
and adjusts enrichment to that. ie amount of fuel - it orders the injectors to stand in line etc.

but the one thing the ECU cannot control and order around is the extra air to go with that enrichment. it can't respond to it and tell it to stay open for longer or slow down or speed up. instead it just gives it the AAV an electric current so it can operate like a clock. and as the clock gets older the ECU can't tell if its gone a bit crazy and lame and just keeps assuming its a fine young specimen of AAV.

it can tell that it has stopped opening the AFM flap but sensor 1 and sensor 2 just keep on going their merry way giving the ECU instructions about engine temp and how to dish up the fuel amount. i don't think it can do much about knowing the flap isn't opening anymore and slap sensor 1 and 2 around. its kind of dependent on its AAV clock keeping correct time without really knowing its doing it.

so the mixture goes off. goes too rich.

i think its the other way from when you unscrew the oil cap.
the oil cap unscrewed immediately leans the mixture and the engine dies.
(it can just suck all that extra air in around the idle bypass screw in the TB).

i think the scenario we are in is the mixture is too rich, and its not getting enough air and its not getting it for long enough. because the fuel marches to the tune of sensor 1 and 11.

which is bad for engine wear if so, so your anxiousness about it is well founded.
you don't want all that fuel in there dumping. you want it burning and warming up fast.

[Van B]

That's right wonki. Bypassing the AFM will throw off the whole fueling equation. It opens more variables than it eliminates. Popping the line to the AAR to check for air draw is feasible once the car is running. But I'm opting for pinching the short line in order to keep everything else accounted for. If pinching that line during cold start makes the condition worse, then to me it makes a strong case that the AAR is not meeting air flow requirements. Conversely, you could say that the engine is being over fueled, but given the objective of higher RPM than normal for engine warm up, such a statement doesn't make sense.

So, I start the car and then pinch the line:
1. RPM increases
2. RPM decreases
3. RPM remains the same

If #1 happens, then it's a lean condition I'm suffering from during warm up. If #2 happens, then it's a rich condition. If #3 happens, then the AAR is already closed.

What am I missing?

Alright, I’m back home today and this morning it was a chilly 4C. So, I was able to give it a proper cold start and do my little test.

First, I started the car as normal and then jumped out and pinched the short line from the AAR to the manifold. To my surprise I only got a subtle 100-ish RPM drop. I unclamped and reclaimed just to be sure, but yeah, that’s all I got.
Also, the car started no different today at 4C than it does at 15C. I thought that was interesting too.

Second, just for S’s and G’s I pulled the line from the boot to the AAR and the car died instantly. And I mean the instant I disconnected that hose. I had no time to even put my thumb over the ends. So, as predicted that is a lost cause.

Lastly, I moved the adjustment pin on the AAR all the way to the outside but got no change. I didn’t expect much really given how cold it is. I’m pretty sure the AAR is as open as it can be.

My thoughts so far:
I’m confident that everything is in fact functioning, but if I want to get the idle higher, I’m going to need more air flowing through the AAR channel during warm up.
Which means, I’m at a dead end for now.

Van

@wonkipop
That theory reconciles with this test. Also, when I ran a tube from the intake boot to the manifold, bypassing the AAV, the idle climbed way high, almost runaway even on cold start.