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

[StarBear]

Opened up and cleaned my AFM a few years ago and again last Spring. No too dirty but did do the eraser thing on the tracks and tweaked the contacts a bit to new material but not very much. (IMG:style_emoticons/default/biggrin.gif)

[wonkipop]

steve, apparently thats not the best way to do that tracking adjustment.
or did you move the plate itself and not bend the arm contact.

what mike told me yesterday.
and also that itinerant article i posted link to.
you have to very careful with that little arm.

having said that, looks like it worked ok when you did it.


----

there was a bit more conversation from mike yesterday.
i didn't include that.
which was.....if you were getting fuel its entirely possible for L jet to run like yours did with the afm unplugged.
for want of a better word there is a kind of limp mode or base line in the ecu that will make the engine go. but it wants to look for input or receive input.
so once it starts running and some inputs come in, like from the CHT, it will go outside parameters without the afm inputs and then just stops at that point.

it was not a detailed conversation. he just said. yes it would go, but it would not take too long before it stopped itself.

i don't know enough and did not press the conversation.
but that thing where yours started strong at 1200 rpm might be how the engine first fires up. off the CHT input. and i guess then the AFM is supposed to send some info too.
but that baseline sure sounds like some basic cold start parameters with a CHT temp input. as if the engine uses that to first start as a baseline which the afm then inputs into with its information. ie confirms it? and off it goes after that with the afm controlling things regarding mixture off the aav. that baseline start would assume a certain air volume into the intake through the AAV opening? but you can think too much into that.

[Van B]

Wonki, those write ups you linked to will be great reference material. I had learned all the AFM stuff from my 944 back in college and even tuned on it a bit back then. But, I’m going to need to source an exhaust gas analyzer. Leaning these engines too much can make them run hotter than you want in certain conditions.

I found a Heathkit exhaust analyzer on eBay that looks real cool. But I don’t know if I should go that route or a more modern wide band sensor that can be used on my 996 as well.
First world problems… I could be getting shelled in the Ukraine right now I suppose.

[emerygt350]

I have recently bought a couple different brands of wideband. Expensive and a cheaper AEM. The AEM is fine. You used to find those for just a tick over 100 in the US. I have found a nice cheap combo where you can buy a 50 Bosch wideband that works with a more expensive gauge that isn't that expensive if you don't buy it with their 110 dollar O2 sensor. If you go that route I can give you the part numbers.

And if you don't want to run wires you can do what I did...



It actually worked really well.

[wonkipop]

Wonki, those write ups you linked to will be great reference material. I had learned all the AFM stuff from my 944 back in college and even tuned on it a bit back then. But, I’m going to need to source an exhaust gas analyzer. Leaning these engines too much can make them run hotter than you want in certain conditions.

I found a Heathkit exhaust analyzer on eBay that looks real cool. But I don’t know if I should go that route or a more modern wide band sensor that can be used on my 996 as well.
First world problems… I could be getting shelled in the Ukraine right now I suppose.

indeed. would not be nice getting putinized.

its good you are of the era fooling with 944s. puts you in a good spot.

my post uni days were screwing around with a twin carb squareback.
erwin rommel era tech.

then i just had cars that ran trouble free for years and didn't need to do much engine diagnostics. even now the renault keeps powering along just fine and its a 2002.
just do cam belts, engine mounts stuff like that. the electronics sides of its been just fine on its own (touch wood).

so i'll be moving into some territory with the 14 soon - maybe - that is a bit new for me.
why all this is of interest. if it turns out to be the case that mine is suffering a similar malaise.

love emery's rear view gauge. thats suave and sensible.

[Van B]

@emerygt350
That’s actually pretty clever… you should call it your RVM-HUD, rear view mirror heads up display!

Ouch… I think I pulled a muscle trying to make that joke funny….

Anyway, I’m actually more worried about finding weldable metal on my original exhaust with regard to a wide band port. That shit is barely hanging in there and I need it to last until I’m ready for that project.

We can’t all be like wonkipop and dine with veteran Porsche mechanics on a Sunday afternoon lol!

[wonkipop]

@emerygt350
That’s actually pretty clever… you should call it your RVM-HUD, rear view mirror heads up display!

Ouch… I think I pulled a muscle trying to make that joke funny….

Anyway, I’m actually more worried about finding weldable metal on my original exhaust with regard to a wide band port. That shit is barely hanging in there and I need it to last until I’m ready for that project.

We can’t all be like wonkipop and dine with veteran Porsche mechanics on a Sunday afternoon lol!

don't get the wrong idea.
mike is way younger than me.
i'm 61. he would be barely 40.
was apprentice of the year back in around 2000.
apparently his special gift was 928s.
he could fettle them naturally, when a lot of guys in the shop he worked in just walked away from them.

he likes big cars, big mercs to be precise. the bigger the better.

my mate max, an old architect has a big collection of cars he amassed over the years,
has never sold anything.

max made an arrangement with mike to look after his cars, run a little workshop etc and mike has flexible hours to be a modern dad and fit in around his high powered wife's career.

its limited customer entry into the workshop. mostly what comes in are cars that bigger shops around town have either given up on, or refused to work on.

some very new stuff surprisingly. and plenty of old stuff. porsches. alfas. quite a few citroens. the mechanics for those are dying out and giving up. and he works on a few old school holdens etc. very eclectic. oh, and the other speciality is original wankel engines, not mazda. he looks after an nsu R080 and a citroen GS birotor. the GS is uber rare. there is only one in aus these days. it comes to the shop every now and then.
a very frail and fickle creature that car.

yesterday was monday. not a relaxing cafe latte set breakfast.
an hour off at the lebanese bakery from fixing the falcon.
and assisting mike to extract the radiator out of a c-6 citroen in between.
boy......what a job that was. most of the front had to come off. french!

i just his pick his mind.
2 years ago when we were bringing the 914 back to life i ran and fetched things and paid attention to him.

earlier he had helped a mate and i do the head gasket job on a citroen xm V6.
with the engine still in the car. supposed to be impossible. we did it.
proved its not an engine out job.

during covid dictator lockdowns i kept him company in workshop and tackled the falcon alongside an merc reconstruction he had to do. bonus for me - he has taught me how to do rust repairs. got a handle on most of it except the welder. got to get more practice on that. i am ashamed since my father was a boiler maker.

so ------ its the reverse of a usual "apprenticeship" working under mike.
i'm older. and i take instruction from a younger master.

he kind of won't really answer questions unless you show a half grasp.
then he tells you where you are wrong, but won't complete the picture.
i'm guessing that is how he was taught and he is reproducing the method.
"don't tell em too much or they will jump ahead too far and get it wrong".

anyway do his afm flap test and post results.
it will pretty much tell you if the aav is still some kind of culprit.
not that you can really fix them --- it seems.

and he didn't say anything about if its the other alternative.
but i'm guessing he would once that test is done and eliminated.

i just go in to the workshop on mondays. i day a week.
once the falcon goes out the door the 914 can come in and sit in a corner for a while as we muck around with it. your R + D will sure come in handy i think.

[Van B]

Would be great if these guys posted up the resolution to the problems they were having:

http://www.914world.com/bbs2/index.php?sho...=355672&hl=

http://www.914world.com/bbs2/index.php?sho...=356316&hl=

@rick 918-S
@SteveL

[Van B]

Time for a little update for the three of you that are still following my quest lol!
I did the alternator change only to learn that the voltage light was due to the solid state Bosch VR not kicking in until some output threshold was reached. Which means that 48yr old alternator was not dead yet (sorry old fella).

Once I finished the alternator, I slapped the AFM on to try the test recommended by Wonki’s friend, Mike. The revs dropped when I pushed on the flap. So, I took the AAV out and started probing on it again.

But, while I had things apart something caught my eye that sent me on a whole other quest. I noticed that the port on the airbox from the charcoal canister was roughly the same size as the ports on the Aux Air Valve (AAV) hook-ups. But, the canister hose was larger. I then dug in the box of take-off parts and found the “original” I replaced on the AAV shortly after buying the car.

See the date stamp on my AAV is from ‘96. But because of the aging on the hoses, I thought they were original. So, when I replaced the hoses, I just got the same size I took off. But they were way too small and must’ve been replaced decades ago which made them appear as weathered as the other original hoses. I had installed 10mm vs 12&13mm hoses which was choking the AAV circuit.

I put everything back together with some 1/2” (12.7mm) hose this time and gave the car another start the following day. The weather has been nice, which is unfortunately bad for testing cold start behavior. But I think I observed a marked improvement in the first couple minutes of running. Idle still drops low, but not to the point of death like it would before.

[wonkipop]

well i don't have any hose mix up issues with mine.
and have the same warm up issue.

so the mike test says its the aav.
we have almost come full circle.

the whole way along i have mentioned this time to time to him,
he raises his eyebrows and says aav.

getting a bigger hose on would certainly help a bit with an aav that has chain smoked 2 packets of marlboro a day since it was 12 years old and is sitting in a wheel chair wheezing.

good work.
sounds like part way to an answer.
your 96 aav is probably in better shape than my invalid unit.

i've managed to convince my mate to let me have that aav i found on his old saab.
he finally realised that car is good to no-one. even him.
we are trying to figure out what else to strip off it before it goes to the great swedish sauna in the sky. his other saab donated an entire D jet system to a lancia he owns and he thinks ahead to situations where you say --- damn, i swear i saw one of those on that piece of crap i had crushed.

[Van B]

My little update is growing, are you all impressed?!

After the shenanigans above, I took off the distributor and installed the Pertronix Ignitor II, new plug wires, new plugs one step up on the heat range (NGK-BP7ES), and then retimed.
I was too advance by 3-4 degrees to make any judgement on how it started then, but I definitely liked the response from that ignitor and how rock steady the timing mark stays when I hold the timing light on it.

Lastly, I pulled the trigger on this guy just for the sake of thoroughness and follow through on the results of the AFM test.
https://www.summitracing.com/parts/smp-ac358

Standard motor calls it the AC-358, but what showed up was unquestionably Bosch!
There is another version, the AC-361 that I would be curious to see what actual Bosch part it is too, but I’m not buying another one just for the hell of it.

Below is a side by side of the original part number and this potential replacement. Observations so far are that they are physically identical on the exterior. However, the valve inside is quite different. The new one is a different shape and is composite material vs metal. Given it was meant for a BMW with twice the displacement, I expect it to flow more, which is what I want!

I’ve decided that I’m going to start a thread for L-Jet people on all the non-standard replacement parts we’ve found that are available to keep thee L-Jets alive… I’m now running a Nissan thermo-time switch and maybe soon a BMW AAV after all.

[Van B]

well i don't have any hose mix up issues with mine.
and have the same warm up issue.

so the mike test says its the aav.
we have almost come full circle.

the whole way along i have mentioned this time to time to him,
he raises his eyebrows and says aav.

getting a bigger hose on would certainly help a bit with an aav that has chain smoked 2 packets of marlboro a day since it was 12 years old and is sitting in a wheel chair wheezing.

good work.
sounds like part way to an answer.
your 96 aav is probably in better shape than my invalid unit.

i've managed to convince my mate to let me have that aav i found on his old saab.
he finally realised that car is good to no-one. even him.
we are trying to figure out what else to strip off it before it goes to the great swedish sauna in the sky. his other saab donated an entire D jet system to a lancia he owns and he thinks ahead to situations where you say --- damn, i swear i saw one of those on that piece of crap i had crushed.

@wonkipop my AAV shows continuity and passes the freezer and hair dryer test so, I don’t know how else to test it. But you can see my post above to know I’ve got no pride in my diagnostic skills. I’ll replace whatever I have to in order to get this thing running like it wa designed to.

[wonkipop]

will be real interested in this.

i think i mentioned came across that old bus blog which had some kind of definitive time on the aav of 8 minutes to fully warmed engne. but it did not say from what temp it started. given it was a usa blog from almost last century i'm guessing maybe colder regions of the states.

my guts tells me it should operate for at least 4-5 minutes here in aus in winter.
given thats how long the engine seems to stumble around for on its cold start mumblings.

its been a while since i tested my aav during recommission.
but i do think it may have been closing faster than that.

amazing that changing a hose relieved some of the strangulation symptoms.
but actually not when you think about it a bit more.

[wonkipop]

well i don't have any hose mix up issues with mine.
and have the same warm up issue.

so the mike test says its the aav.
we have almost come full circle.

the whole way along i have mentioned this time to time to him,
he raises his eyebrows and says aav.

getting a bigger hose on would certainly help a bit with an aav that has chain smoked 2 packets of marlboro a day since it was 12 years old and is sitting in a wheel chair wheezing.

good work.
sounds like part way to an answer.
your 96 aav is probably in better shape than my invalid unit.

i've managed to convince my mate to let me have that aav i found on his old saab.
he finally realised that car is good to no-one. even him.
we are trying to figure out what else to strip off it before it goes to the great swedish sauna in the sky. his other saab donated an entire D jet system to a lancia he owns and he thinks ahead to situations where you say --- damn, i swear i saw one of those on that piece of crap i had crushed.

@wonkipop my AAV shows continuity and passes the freezer and hair dryer test so, I don’t know how else to test it. But you can see my post above to know I’ve got no pride in my diagnostic skills. I’ll replace whatever I have to in order to get this thing running like it wa designed to.

yes there really isn't any test further than that other than having a good sense of/solid information of - time to take to close. thats all down to the heater coil element inside.
which repeated dose of electricity and warming weaken. so it closes too fast as a result.
ie expands too fast.

the 8 mins is the only thing i have stumbled across.
but i figure so long as its open and so long as it ultimately closes, then it does good the longer it takes so no need to be exact. 8 minutes is a good warm up.
2 minutes is death by oxygen deprivation. which has got to be a good part of the problem.

[Van B]

Tomorrow, I will cold start and go for a drive. Then change out the AAV and try it again on Saturday morning. Or since you’re 14hrs ahead, you could just tell me how it all worked out!?!

[wonkipop]

Tomorrow, I will cold start and go for a drive. Then change out the AAV and try it again on Saturday morning. Or since you’re 14hrs ahead, you could just tell me how it all worked out!?!

sounds like i should seriously consider getting rid of the points and doing the petronix ignitor. this variant you mention replaces the points?

i pulled out the crystal ball. its on the blink. the ruskis are jambing it.

[Van B]

Tomorrow, I will cold start and go for a drive. Then change out the AAV and try it again on Saturday morning. Or since you’re 14hrs ahead, you could just tell me how it all worked out!?!

sounds like i should seriously consider getting rid of the points and doing the petronix ignitor. this variant you mention replaces the points?

Yeah, and though I haven’t driven yet, I’m so far impressed. It replaces your points with basically a Hall effect sensor. As such, I have expectations for improved high RPM performance. For sure throttle response is noticeably improved as well as dwell stability under a timing light. With the points the timing mark would just kind of wiggle and oscillate ever so slightly, now it’s rock steady.

[emerygt350]

Going solid state (123 in my case) was one of the best things I did with mine. I loved the idea of going back to points but in reality, modern stuff is soooo much better. My old dizzy can sit on the shelf as a conversation piece.

[Van B]

Guys, I think I have the cold start sorted. Not just back to the OE performance level that @StarBear and @wonkipop showed with their timed examples, but a proper high idle warm up!

Along this journey I discovered several key issues:

I had poor injector spray pattern that was causing wash down on real cold days. It would manifest itself as a dead cylinder until the engine got warm enough to make the fuel sizzle and then it could ignite the vapors. Solution here was 4 NOS tested and flow matched injectors with a verified spray pattern. (I bought 7 to get those 4)

I had Bosch spark plugs that did not seat. The taper below the hex was hitting the shoulder on the recess for the plug prior to the plug seating and allowed compression and fuel/mixture to escape through the threads. Solution here was NGK plugs.

I had a dead thermo-time switch that meant I wasn’t getting the full 8 seconds off the cold start valve on actual cold days. However, it should be noted that the CSV does function while cranking even with a bad TTS.

I had hoses to and from the AAV that were 3mm too small in diameter. I got baited into this mistake by replacing the hoses based on the size of the old hoses I pulled off. They were old and nasty same as everything else in the engine bay so, I just assumed they were original, and correct. They were not.

And finally, the AAV I bought as an experiment has given me the ideal high idle! It’s meant for and ‘87 BMW M5. Externally, it is the same as the OE part. Also the passage is the same size. But what is different is the shape of the valve. It allows more air at all stages less than full open compared to the stock part.

So, with all the above, and even on a warm 75F/25c day, I got a full 8min of a steady 1300RPM warm up! This is in contrast to my start yesterday, which after reading back through this thread, was pretty on par with what the guys described on their car.

More details on request (IMG:style_emoticons/default/beerchug.gif)

Van

[wonkipop]

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

the spray pattern of injectors is an interesting side note.
i have not / did not have the bosch injectors i got in from USA tested.
just whacked em in and it went well.
but......if i have troubles with mine after i get stuck into it with all this data you have so generously supplied along the way, i can take a look at that too.

i'll go on a mission to get hold of as many of those similar AAVs i can find here,
to give myself some options.

nice work going at that for as long as you have and as rigorously.