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

[emerygt350]

This kind of knowledge storage is awesome, but a little scary. I wonder what will happen in the long run. Will this all be lost since it wasn't on paper ...

[wonkipop]

This kind of knowledge storage is awesome, but a little scary. I wonder what will happen in the long run. Will this all be lost since it wasn't on paper ...

i guess its here now on this website.
lasts as long as the website? which has been around for a while.
which ---is a kind of new book?

van's pursuit of cold start issues also provoked the dig into 74 1.8 L jets.
we kind of got to the bottom of it, for 74 at least, - thats in the history/originality section now.

certainly more here on this website than there is out there in the published paper world. ......and some of whats out there in books can be seen to be inaccurate information as time goes by and more detail surfaces. not the fault of those writers, they just did not have access to a broad enough sample of the cars out there to notice things or see much in things.

guess the L jet cars were in the shadow of the earlier D jets and also the concentration on the 2.0L 4s as the desirable variant?

EDIT
ps - thats why its worth $30 usd in fin. support a year.
not many technical subscriptions at that rate offering this kind of value for money?

[Van B]

flum·moxed
/ˈfləməkst/
adjective
adjective: flummoxed
bewildered or perplexed.
"he became flummoxed when his 914 continued to struggle on cold weather starts”

So, tonight’s attempt required several seconds of cranking, then slowly lumbered to life at a very low RPM. It required two touches of throttle to keep it running in the first minute or so. But then it started to steadily climb out of the hole, which is a new behavior . I just don’t get it! I’ve only got another month of actual cold weather and so I really want to crack this!

So far this quest has uncovered a litany of issues; most of them attributable to improper maintenance. And most importantly, performance when warm has substantially improved. But I am convinced that the cold weather start struggle has multiple causes. Unfortunately, the only thing left for me now is to dig into the engine.

[wonkipop]

there is only the AFM left to go?

it could be in there.

mine almost does what you describe.
but it does not struggle to life.
it springs into life (for about 10 seconds) and then subsides into the hole.
which it then digs itself out of as per yours.
it takes around two minutes to get up over the edge of the hole.

and then when its warm it runs just dandy.
as it always has.

apart from that hunting thing on a low tank of fuel.
but i am right hand drive which has its own unique problems of my own making.
but i have a full theory/explanation for that now which i shall go into after i reinstall my rebuilt original fuel pump and reroute a couple of fuel lines down there near the fuel pump.


starbear cleaned out his afm. he wrote me a pm about how it mortified him doing it.
he knows how to do it.
his does not seem to suffer this fall into a hole problem like ours?

[emerygt350]

Any of you 1.8people have an O2 sensor installed?

[StarBear]

Not that I’m aware of, though after 48 years still learning about these little contraptions.

[wonkipop]

Any of you 1.8people have an O2 sensor installed?

no.

ie lamda sensor in the exhaust?

even the 75s with cats didn't have one.
no feed back loop in these early L jets.
they are called open systems.
don't think they went to closed loop L jet until very early 80s.


it does however take an input from the AFM at start up in two ways.
there is an air temp sensor in there.
and while the AAV is open its going to be drawing additional air and moving the AFM flap open slightly.

i figure that if the stamped circuit in the AFM is worn slightly or dirty right at that first part it could be affecting things. ie it gets extra fuel at start up by virtue of almost simple clockwork. aav is open, that pulls AFM flap open a small amount and signals to the ECU that the flap is open give it more fuel. and if its getting no air temp input properly that might be upsetting things too. ie no signal to the ECU that incoming air is cold. all its getting is a signal from the CHT - and its not enough? i'd have to think about it more.

its a possibility. van has been through everything else.
CHT, AAV, new injectors, he has done it all. timed it. tuned it.

once the car is warm it does not need that extra bit of air and fuel so it is content to idle through the idle port in the AFM? and does not need the extra air and flap open at all.
and you rarely (ie never) drive the car at 1200 revs so you never notice that bit of wear or dirt on the AFM?

a thought. can't think of anything else.
and mine is very similar.
everything is hunky dory when its warm.

[StarBear]

“Everything is hunky-dory when it’s warm.” Kind of like us ‘mature’ folks, eh? (IMG:style_emoticons/default/biggrin.gif)

[emerygt350]

No, I mean for knowing your afr. I have one in my djet engine to help me tune it. If you had one you could see if it is a fuel ratio issue at cold start. Too rich? Too lean? Helps figure out what is going wrong.

[StarBear]

No, I mean for knowing your afr. I have one in my djet engine to help me tune it. If you had one you could see if it is a fuel ratio issue at cold start. Too rich? Too lean? Helps figure out what is going wrong.

We have a CO adjustment screw; that’s all though doubt many of us have a meter.
How does the O2 sensor provide a useful monitoring info? Ties into a meter reading somehow? An interesting idea….

[emerygt350]

Knowing it is too rich or too lean can point you to the issue (if it's fuel related). Also as the car warms and starts to run well you can see if the afr is changing appropriately. Just more data points.

[Van B]

No, I mean for knowing your afr. I have one in my djet engine to help me tune it. If you had one you could see if it is a fuel ratio issue at cold start. Too rich? Too lean? Helps figure out what is going wrong.

It would be a very handy diagnostic tool for sure. I don't want a gauge/dash setup but I would like to have one that could run as a stand alone with a probe or with a bosch wide band sensor. When I built the exhaust for my 996, I installed extra bungs just so I could have that option down the line. that car only has narrow band sensors so the data from them is not real helpful.

Regarding the 914 and @StarBear 's question, it would have much less usefulness for tuning and without another car with a confirmed functioning cold starting feature to compare against on the same day with the same temps, it would be tough to know what the numbers mean. I mean technically, I would see the values, but how much enrichment am I looking for, ya know?

[wonkipop]

its way dumber than that @Emerygt350 .

you can adjust things after the engine is warm.
the CO screw does all that.
and you could additionally measure O levels with a probe.
but......may not help for the warm up.

from what i have read the warm up enrichment is controlled by 3 things.

1. CHT. Van has already put in a new one.

2. intake air temp sensor in AFM.

3. movement of the stator flap in the AFM (which would be drawn slightly open by the AAV being open).

#2 influences and modifies the signal sent by #3 to the ECU. so that intake air temp sensor has an effect on the signal generated by the stator flap and the ECU can recognise the engine is cold and even further to that it is drawing in cold air. logic tells me that is what sends it into the cold start regime. part of the input is the CHT. but there is also input to say stator flap is slightly open (AAV pulls it open but as a piece of "clockwork"). and the ECU recognises those two additional inputs, stator flap and cold intake air. ie it can also distinguish that the stator flap is open in a cold air situation. together all three switch a circuit(s)in the ECU that is the full cold start regime?

how you can adjust that alone is i think not possible.
you can adjust CO at warm idle and you can adjust CO generally i think at ECU further.
i'd have to check up on our ECUs for 1.8s again. but that is not going to help at warm up as its got an internal "routine" so to speak inbuilt in the ECU if you could call it that.

so i think an air temp sensor in AFM or the printed circuit the stator flap sweeps over could be a culprit. it would be in that section of the first part of the stator flaps movement. the open AAV would not be pulling the stator flap very far open at warm up.
but if its not getting the correct electrical signal generated by that first part of the AAV flap movement it is definitely going to affect enrichment. it might be worn or have residue built up on it.

there is some proceedure to clean that printed circuit in there.
i've come across it here on this website.
how to open up the AFM and do that.

as to the temp sensor in there.
somewhere i have an L jet tech manual that tells you how to test it.
but.....having said that it then says that if it is defective it cannot be repaired.
however - as we know 914 owners seem to be capable of rebuilding just about anything at this stage that previously were regarded as unfixable and to be thrown away.

------

down at the workshop i can get hold of an exhaust gas analyser.
a real old piece of equipment. we use it to tune all the old cars.
but there is something that needs fixing on it at present.
we have been borrowing one from the mechanics across the road.

i'd have to leave the 14 down there overnight and then do a cold start fire up.
i think that would give me the values you are talking about emery?
whats going on at cold start in terms of the air fuel ratio.


-------

i've got a good CHT i have tested.
i've got good injectors that work perfectly.
i've got a good cold start injector and temp switch that works perfectly.
i've got an AAR that opens but i suspect may close too quick.

and a similar set of symptoms to vans car at cold start.
and a similar set of components i know to be close to as good as the ones van has in now.
(i'm guessing if i was in maryland or cold cold north america mine would really fall in a deep hole too for the first couple of minutes just like vans).

and i'm think with mine when i get it into the workshop for the fuel pump fiddle that i will see if i can do the tests on the AFR and maybe even open it up and clean it if necessary.
i can test the temp sensor too, but what i can do about it i don't know if its not right.

[emerygt350]

Well, something is up. Knowing couldn't hurt. Pretty much every car wants the same thing as they warm. 10:1 at the start (csv) rapidly leaning to about 12:1 (cht) then a slower rise to 14:1 (at idle). I know at idle wide bands are not great but in both my 84 FI mustang and the 2.0 914 they follow the same pattern. Both run about as good as they can (the mustang probably better than it was ever meant to).

[emerygt350]

Temp sensors can be tricked with pots and resistors...

[wonkipop]

Well, something is up. Knowing couldn't hurt. Pretty much every car wants the same thing as they warm. 10:1 at the start (csv) rapidly leaning to about 12:1 (cht) then a slower rise to 14:1 (at idle). I know at idle wide bands are not great but in both my 84 FI mustang and the 2.0 914 they follow the same pattern. Both run about as good as they can (the mustang probably better than it was ever meant to).

good general info - thanks for that emery.
i'll try and get mine on a machine with the exhaust probe and see if i can get some comparative measures. got to get the ford falcon out of the way to make room to leave it down the workshop. not far to go.
it will be a bit cooler here soon in autumn so i can get a better guage on cold starts again.

[Van B]

Manual doesn’t tell me what pins to check for temp sensor 1. The 912E also isn’t helpful because it’s a 7 pin connector.

[Van B]

Without the tester specified in the manual, there are only two resistance checks I can do, and I don’t even know what they mean. But I do know that mine is within spec on both readings.

[wonkipop]

try this.
its from another L jet manual i have.
unfortunately there is no real separate test it seems for temp sensor 1 distinguishing from potentiometer test. both are same?

[wonkipop]

looks like your info is same as mine.

if you tested it and it is ok that is good news.
means your temp sensor 1 is still ok.

it could be the worn track thing on the inside.
i need to find that thread here about cleaning it.

i'm sure starbear told me he did open his up and this cleaning proceedure.