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

[StarBear]

@Van B didn’t get hone till late and snow/ice tonight and tomorrow so might not get to it until Saturday or Sunday. If I recall in the past, when I did the same it just cranked and never turned over (informing me I had not reconnected it).

[wonkipop]

A weird thing happened last night. I went out to start the car, mostly out of boredom and frustration... and after cranking a few times it fired up and jumped to 1400 RPM! As I sat there in existential confusion, it slowly climbed to 2000 RPM. At that point I got a little concerned and blipped the throttle and the car cut out and died.
So, like a good little monkey, I started the car again. Same result. That's when I realized I never plugged in the 6-pin on the AFM after testing it the day before. So, I plugged it back in and started the car once more. This time it started and went to a normal idle. No doubt the resulting normal third start was due to the fact that it was warm out and the car had already warmed up sufficiently.

What I'm struggling with now is that this happy little accident has seemingly ruled out a mechanical fault. I mean other than taking more cranks than what most people report as the norm, when it started with the AFM unplugged, it behaved just like my 996 for the first few seconds... a smooth high idle.

@wonkipop @StarBear would either or both of you be willing to replicate this experiment for me on a cold start to act as a control? In other words, would you unplug your AFM and attempt a cold start and let me know what happens? I would like to know whether this behavior is atypical or if it's standard.

Van

wow, yours started with the 6 pin out.
i already know what happened with mine once.
i changed my air filter out and forgot to plug it in.
no start.

i can try again later when i have a moment and see what happens to double check that.

[wonkipop]

As long as the points go, you should be better off.

Funny thing on these engines is the rev limiter is kinda useless. It's the overrun that will blow your motor.

right on.
that rev limiter rotor was/is a waste of time.

fyck up a gear shift and bye bye engine despite the stoopid rotor.

[wonkipop]

@Van B

those you tube videos with AFM - you can see the little track i was talking about.
with the sweeper.

people sometimes go in and make sure the track is super clean and also adjust the sweeper very slightly so it runs in a different spot.
it can wear a groove as years go by.

however i don't think this would be affecting warm up idle.
but maybe if the first section of track is a little worn its possible.
be right at the start of the track.
that is one of the connections between the flap and the ECU that is important to the ECU knowing where the flapper really is and how much air is coming in.

------

[Van B]

Like I said earlier, I pulled the top off and everything looks new in there… brand new. It’s a rebuilt unit from Fuel Injection Corp.

And yeah it started but any touch of throttle would kill it. So, clearly fuel injectors are commanded to send fuel even without the AFM. But there was no way for the computer to adjust fuel.
What was really bizarre was the high idle and that it jumped right to it from a first start.

If y’all can at least try it, it would be much appreciated.

[wonkipop]

Like I said earlier, I pulled the top off and everything looks new in there… brand new. It’s a rebuilt unit from Fuel Injection Corp.

And yeah it started but any touch of throttle would kill it. So, clearly fuel injectors are commanded to send fuel even without the AFM. But there was no way for the computer to adjust fuel.
What was really bizarre was the high idle and that it jumped right to it from a first start.

If y’all can at least try it, it would be much appreciated.

i'll give it a shot later.
have to get the renault out of the way.

will report back when i have done it.

[wonkipop]

ok

i just did it.

it started.
straight away like it does connected.
one crank and bang it went.

i touched nothing like i usually do.

did not go to high revs.
was at about 850 rpms.
then stopped on its own after about 10 seconds.
never got higher than 850.

i reckon it ran off the cold start injector.
reminded me of the time when we recommissioned it and the same thing happened.
fired straight up, ran for 10 seconds then stopped.

so i don't believe i was getting an injector signal when i just did that.

i remember now when i last did the disconnect thing accidently.
it fired up and then stopped.

i reconnected it.
did a normal (ie abnormal) start.
ie it went weak for that first 2 minutes and then came on.
but it needed that plug in for the regular injectors to be signalled to fire.


so--------this is gettng real interesting now.

[Van B]

So mine ran for several minutes without the AFM plugged in. It definitely was not the cold start injector that kept it going. That thing can’t put out enough fuel to support 2k RPM.
But it is interesting you didn’t get a fast idle… I’ll see what results Steve gets. I don’t yet know if this is a thread I can pull on or not. But I can’t get past the fact this is the first time the car did not struggle on cold start.

[emerygt350]

Wow, I think you guys are on to something! No idea what but this definitely looks like a worthy lead.

[wonkipop]

after reading one of your posts a few back where you mentioned the 912E manual you were looking at, i searched that up.

came across something i thought was interesting.
they really changed the characteristics of the cold start injector and thermo switch on the L jet 912 2L.






its currently 19.8C right now in melbourne.
maybe its a little cooler in the garage.
but its definitely not 13C out there.
and it definitely ran off the cold start injector for sure when i fired it just then and nothing else. but who is to say that info there is strictly correct from that manual.

point is i found it interesting that they really beefed up the cold start for the 912E.

[wonkipop]

So mine ran for several minutes without the AFM plugged in. It definitely was not the cold start injector that kept it going. That thing can’t put out enough fuel to support 2k RPM.
But it is interesting you didn’t get a fast idle… I’ll see what results Steve gets. I don’t yet know if this is a thread I can pull on or not. But I can’t get past the fact this is the first time the car did not struggle on cold start.

yeah no way it was the cold start injector.
yours ran.

and that is very different.

[wonkipop]

well we know you have a good strong set of new components in yours van.

van.

cht.
injectors.
afm rebuilt.
everything checked. aav. cold start. thermoswitch etc.

wonki.
injectors is all that is new.
the rest of mine is just checked. (2 years ago).
i have an afm i reckon that has never been opened.
no evidence. i have never opened it. had it for 30 odd years.
doubt it was ever opened before i got it.
i could have had a component deteriorate since 2 years ago.
and will recheck all shortly once falcon is out of the way. cht. aav etc.

its possible mine might run like yours but something stopped it since the engine was cold. a now defective cht? hard to know. ie something did not indicate to the injectors to fire more fuel than when warm. so not continueing to run or go to high revs could be down to that. and it merely mimicked the stuffed injector scenario of 2 years ago.

definitely only wanted to go for that 10 seconds and cold injector would have let it do that then not enough fuel to persist beyond that.

be interesting to see what steve's does.

-----

alternatively there is some scenario with yours where it is firing the injectors and that is not normal.

i'd have to do some more reading again to work out what signals the injectors when its all proper.

[wonkipop]

ok you got me thinking.

there is a variation on this exercise i should do.
warm start it with the plug off.

that will tell me if i am getting some kind of injector signal which does open the injectors to run the engine or not to cross check against what happened to yours.

if it does the same trick of not running then i know i do not get injector signal for sure with the plug off.

[Van B]

Regarding your 912E reference, that is entirely determined by the thermo-time switch. Essentially, what that manual says references a TTS that is NLA.

You can see here that my old dead switch was a 35c switch (912E). The new Nissan switch is 19.5c. But both are still 8sec.

[Van B]

Wow, I think you guys are on to something! No idea what but this definitely looks like a worthy lead.

I hope so. Wonki is a research monster so, I definitely need that right now. I can’t believe how there’s just no info on all this after 48yrs of 1.8L 914’s on the road.

[wonkipop]

yeah van

but what i have been thinking is that 1.8 L jets were burdened with a marginal right on the edge warm up from the start.

that just worked. right on the edge.

reason i say that is all that EPA stuff i stumbled across on EC-A/EC-B research.

i think the EPA monstered VW into a warm up procedure that turned off these thermo switches at anything over that 68-65 F temp that was the low end of the EPA test range.

there is slightly varying info on the 914 1.8 cold start thermo switch.
but i think the general gist is its fully operational at under 55 for the full 10 or 8 seconds and from 55 to 65/68 it operates increasingly shorter time until at 68 theoretically its off.
but mine certainly worked this morning. but maybe it was cool enough in garage to be down there for it to flow for a good 5 seconds and dump enough fuel for the motor to run for about 10.

then a couple of years later i think the EPA relented and let porsche/VW have a thermo switch that was activating for cold starts above 65/68 F test temp so long as they could prove it was a cold start only and operated only for a max 10 seconds.

i think that is a really big change on the 912E. for fundamentally the same motor and EFI system. its a way bigger margin the cold start works in temp wise and i bet it dumps in a whole lot more fuel during that period it activates.

....and they must have wanted to make that change for a reason.?


i think they were really getting leaned on by the EPA.
right about the time the poor 1.8 was being worked out.

i think everything working fine and when brand new it warms up.
buts it right on the edge.
and it maybe never really did the kind of warm up we get in more modern cars.

the vac retard is pulling the timing back.
the aav has to work perfectly.
if your timing is out by a bit, or your points clagged or gap wrong.
the wiring is degenerating etc.
and then its got zero safety margin and starts to get frail trying to make the motor run cold.

reason i say this is everything settles down fine on mine once its managed to get warm.

i'm really trying to remember what mine was like 30 years ago.
i don't think it was as weak as it is now, but i don't really recall a time when it fast idled up really strongly from cold.

what we need is an old timer like the late cap'n krusty with a vivid recall to tell us what they were like just out of the showroom. but all those old timers are passing away.

i'm still thinking my aav is some kind of problem.
and i am going to rig up the garden tap gizmo that emery has to test with.

but this thing where your car ran without the plug has me really thinking.

[wonkipop]

re those thermo switches.

the temp rating means at that temp on them they work for whatever it is.
8-10 seconds. its a certified measure.

as current warms them up or engine heat warms them up they reach a cut off temp that closes them. the cut off temp is not the temp inscribed on the switch.

they take time to reach that cut off temp as well.

i'm betting the 914 works approx like this.
at 55 its on for approx 10 seconds.
and by 65 (or 68) its off.
and it takes about 8 seconds to get to that cut off.

that kind of spec would meet the crazy demands of the EPA in 73.
68F was the temp the EPA was obsessed with.
anything could switch on under that temp for a cold start, but above that temp they saw it as outside "the law" when they cracked down.

VW used 65 F to give themselves a safety margin on EPA edicts.

meaning - start your car at 60 and it fires for about half that time. say 4 seconds.

and below 55 it can theoretically fire for even longer because its going to take longer to hit 65. hence references you find to it operating for anything up to 20 seconds max.

once the electricity hits it it will reach 65 and cut off no matter what, from a really cold temp even well below 55 by about 20 seconds later.

thats my take.

but then they come along with the 912 and they want it to work at a higher temp for that 8 seconds. which means it must fire for longer when its down at that lower temp of say 55? and the EPA must have relented and said, yes you can have that, its only on for 10 seconds, we will allow it, it cannot operate as cheat device, etc.

or is my logic out here?

whatever it is they wanted more fuel dumped in the 912 for longer and at even higher ambient temps to get it going.

------

i might be a research monster but i can only find stuff experts have written.
and there is sweet F A out there on these early L jets covering this particular problem.

it seems 928s suffered a bit from something similar.
and there is discussion in forums about symptoms not unlike this with ours.

i need to find out more about 928s of which i know zero.
i think they have an AFM and not a mass flow meter like late 70s 911s.
but i don't really know.

i do know that 964s have an AFM with flapper just like ours.
porsche reverted with those.
it didn't work too well i believe as they like blowing up their AFMs from stories i have heard. bit of a big backfire and its all over in there.

[djway]

If you are starting without the pin hooked up you should be running solely on existing fuel pressure as your pump shouldn't work.

[Van B]

If you are starting without the pin hooked up you should be running solely on existing fuel pressure as your pump shouldn't work.

I would’ve said the same thing prior to this, but it ran for a good while. At 2k RPM mind you.

@wonkipop
I can attest that when the thermo time switch is above the rated temp, the circuit is open. As for it ever allowing the CSV to run longer than it’s rated 8sec. I doubt it. But, it would be testable.

As for my current status, technically, I haven’t ruled out a temp sensor 1 issue. As the two resistance tests in the manual only say to test between pin 6 & 9, and 7 & 8 with no explanation as to what those readings are confirming. I think I will call fuel injection corp and ask them.

Further, the way the engine ran when the AFM was unplugged had no stumbling or anything like that. It was smooth and consistent. Which means, I need to drop the theory on a mechanical fault.

For now, I just need to think about what just happened and understand if it is an exception or if other 1.8’s do the same.

[wonkipop]

re running without the pin hooked up and fuel pump.

mine had been sitting since last sunday.
it was friday today when i did the pin out test for van.

i dunno, i think the fuel pressure would have subsided in the lines.
but i don't know.

the pump shuts its valves and i suppose there is pressure in the circuit.
it maybe does maintain just enough after 5 days bleeding down.

its an interesting point you make djway.

i could have used up all the residual pressure in the line when i did the plugless start.

i did not think to do it twice. that would have demonstrating something.
i am a dummy.

should have tried it a second time with the plug out after it quit.
would have answered that one.

i can try again on the weekend.