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

[Van B]

I pulled the cover and it’s nearly new in there. It’s a rebuilt unit from fuel injection corp.

I mean it, I cannot think of any other system aspect to check. The only roads left are mechanical.
It’s not like I haven’t made steps through all this by finding and addressing substantial issues, but nothing has solved the cold start issue.

[Van B]

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).

I would say these are the numbers of a well tuned engine. I think OE tunes are generally a bit too rich (high 12’s)

[wonkipop]

is the flap moving freely in the intake plenum chamber.
can you sense any hesitancy from the closed position.

just wondering it if could be sticking and the aav is unable to pull it open at cold start.

sticking with the idea that what triggers the a f r mix is the air flow in L jet.
(yes there is temp input, but its in parallel with the flap being moved).
i mean that is all i can see that triggers the enrichment for cold start up.
those two sensors and what must naturally occur if the AAV opens which is the flap moves in the air flow meter to let in additional air or send the signal that additional air is coming in. if its not getting the signal that additional air is coming in then temp sensor 1 can do all it likes to modify the signal but the signal would be saying no add air is incoming.

or am i thinking this wrong?

[wonkipop]

am thinking there is one last test you can do.

it should be possible to undo the aircleaner, get the base out of the way and prop the top half so you can see inside to the flap. do a cold start and go have a look and see if its pulling the afm flap open during that first initial part of warm up.

sit there and watch it. see if the AAV is doing its job and pulling that AFM flap open.
and watch to see if it closes right up again when its warm. it should since by then it will be running off the idle passage through the AFM. to my way of thinking it cannot be doing initial warm up through the idle passage alone?

this should not disturb anything or cause any air leaks.
and its the last mechanical test of all components.

if that flap is puling open then its got to be something not getting that signal through to the ECU. or in the ECU itself? because you have crossed everything else off the list?
as far as i can tell anyway!

i admire your commitment to the cold start.

[Van B]

It moves like it’s made of butter. But I don’t see any reason not to lay eyes on it during a start up.

My commitment to this is that I believe a real cold start brings out issues with an engine that may otherwise be masked in more favorable conditions. That’s how the “cold start” became such a classic proof when selling or buying a car.

Just look at all I’ve uncovered during this pursuit:

-Spark plugs that weren’t seated
-Faulty fuel injector
-Incorrect engine timing
-Incorrect setting on decel valve
-Bad thermo time switch
-bad voltage regulator
-wrong charcoal filter pellets (leaking into the intake)
-cracked intake boot
-cracked vacuum lines
-pinched and twisted fuel hoses

And since I still have this cold start issue, I know there are more problems to discover.

I’m just tired of striking out. I can’t really say I’ve enjoyed my 914 ownership so far… especially when I have this beast of a 996 sitting next to it that is always ready to party!

[wonkipop]

It moves like it’s made of butter. But I don’t see any reason not to lay eyes on it during a start up.

My commitment to this is that I believe a real cold start brings out issues with an engine that may otherwise be masked in more favorable conditions. That’s how the “cold start” became such a classic proof when selling or buying a car.

Just look at all I’ve uncovered during this pursuit:

-Spark plugs that weren’t seated
-Faulty fuel injector
-Incorrect engine timing
-Incorrect setting on decel valve
-Bad thermo time switch
-bad voltage regulator
-wrong charcoal filter pellets (leaking into the intake)
-cracked intake boot
-cracked vacuum lines
-pinched and twisted fuel hoses

And since I still have this cold start issue, I know there are more problems to discover.

I’m just tired of striking out. I can’t really say I’ve enjoyed my 914 ownership so far… especially when I have this beast of a 996 sitting next to it that is always ready to party!

joy of a vintage car van. (IMG:style_emoticons/default/smile.gif)
its half a century old, and you have sorted out a ton of dickskull mechanical work done by others and general decline reversed.

i've got a little renault RS clio i can take out anytime and its always up for a party.
as per your 996. mines a wolf in sheep clothing. cops don't even look twice at it.

but the steering feel will never equal the 914.
esp since i stuck the 165s on the 14.

i'll put up with the warm up in mine if i can't solve it.
sounds like i might hit the same brick wall as you.

(IMG:style_emoticons/default/beerchug.gif)

PS - the other way to look at it is that L jet is such a heroic bit of wartime style engineering that it can keep the engine going even though some component is letting it down. like a machine gun full of dirt that just keeps on firing.
rather than seeing it as a fault its like something that just won't give up even in old age.

i'll use emery's handy figures on what to look for roughly on a f r by sticking a probe up its tail pipe on a cold start and see what happens. i figure if the a f r is ok when its all warm and operating normally then its not suffering any damage during normal use.

its important not to be tempted to put too much boot into it when its cold via the accelerator as you can get a backfire and that will do the AFM no good at all.
its a balancing act to get it up to temp and oil circulating but also avoid the back fire.
mid 70s 911s used to be famous for blowing up their airbox and doing all sorts of damage on a cold backfire even down here in emission free (relatively speaking) australia in the easy going "she'll be right" era long past. i think they ran K jet. but i don't really know. 911s have always been outside my budget. and now they are so outside it they are in another universe. but a mate of mine has one. a 75. had it since new. he never sells any of his cars. he has some technique or mod to his airbox so it blows the hose off before it blows anything else up. i think its as dumb as not having a hose clamp done up too tight. only he is allowed to do up the hose clamp.

[wonkipop]

this is of interest van.

in 5 parts.
guy with an l-jet opel manta tuning the afm.


https://www.youtube.com/watch?v=PqEBgS6hSGQ

[StarBear]

(IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/beer.gif)

[Van B]

this is of interest van.

in 5 parts.
guy with an l-jet opel manta tuning the afm.


https://www.youtube.com/watch?v=PqEBgS6hSGQ

Yeah, I’ve seen those videos. Would love to have those tools!

[wonkipop]

this is of interest van.

in 5 parts.
guy with an l-jet opel manta tuning the afm.


https://www.youtube.com/watch?v=PqEBgS6hSGQ

Yeah, I’ve seen those videos. Would love to have those tools!

yeah i want his a f r machine.
have to keep my eye out on ebay.
was especially into the way it had CO arrayed at bottom as well.
it had it all in a nice little box.

we have got a much bigger version and just as analogue down the workshop.
it looks like it dates from the 1970s.
but there is something wrong with it that needs fixing.

[Van B]

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

[emerygt350]

Very interesting!

[Van B]

Very interesting!

To put it mildly.
I plan to mess with the points settings tonight and see if that changes anything. From reading the manual, .4mm is the start setting, and .3mm is the minimum. I don't have a fancy dwell machine, but I think I'll move the points gap in and out and see what changes... if anything.

[rjames]

Very interesting!

To put it mildly.
I plan to mess with the points settings tonight and see if that changes anything. From reading the manual, .4mm is the start setting, and .3mm is the minimum. I don't have a fancy dwell machine, but I think I'll move the points gap in and out and see what changes... if anything.

They aren’t that fancy. Don’t guess at the setting. You should be able to find a dwell meter for ~$20.

[emerygt350]

I have an ancient dwell meter from back in the 80s when I had an opel. Critical equipment. My opel wasn't that sensitive to point misadjustment but the 914 was super sensitive. So sensitive that the 123dizzy was a god send...

[StarBear]

@Van will do and let you know.
Yes, get a dwell meter. I find mine is very sensitive.
EDIT: Spec is 44-50 degrees; I get mine right on 48 though takes several attempts even starting with gap tool.

[Van B]

I have an ancient dwell meter from back in the 80s when I had an opel. Critical equipment. My opel wasn't that sensitive to point misadjustment but the 914 was super sensitive. So sensitive that the 123dizzy was a god send...

My math runs like this:
Pertronix > points+dwell meter

I placed an order for the Pertronix Ignitor III with built in rev limiter. In this way I can remove points from the equation entirely.

I don't see enough info on the L-Jet out there for me to pull the trigger on the 123ignition just yet.

[emerygt350]

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.

[Van B]

you mean the ole full throttle 4th to 3rd? That should be near impossible on a bolt action shifter like the 914 lol!!

[StarBear]

I have an ancient dwell meter from back in the 80s when I had an opel. Critical equipment. My opel wasn't that sensitive to point misadjustment but the 914 was super sensitive. So sensitive that the 123dizzy was a god send...

My math runs like this:
Pertronix > points+dwell meter

I placed an order for the Pertronix Ignitor III with built in rev limiter. In this way I can remove points from the equation entirely.

I don't see enough info on the L-Jet out there for me to pull the trigger on the 123ignition just yet.

A lot of us 1.8s have had trouble getting Petronix to work; others no problem. (IMG:style_emoticons/default/confused24.gif)