peanut

yes I couldn't remember what it is called on the early 944s either I think it may be aux air valve ? anyway we all know what I am referring to and it is a key component the ECU uses to control the idle mixture .

Jacob AbuKhader

Ah this is the electronic valve under the intake manifold on my car I believe.

There is also an idle control valve that is in the vacuum loop. I’m a tad busy at the moment but I know what your referring to. When I get a chance I’ll pop the hood and take some pictures for anyone using this thread as a guide. Should have titled it the “ultimate 944 intermittent test guide”. Are there any procedures for testing it or am I stuck yet again needing to swap in a “known” good unit? From what I understand there’s a temperature sensitive spring inside it. The ECU runs current through it when the engine is cold and by the time the engine reaches temp, the spring contracts and closes the valve. Correct?

Spring44

Wow, this is such a head scratcher. The symptoms that you describe (runs good initially, then dies, sits for a bit then runs ok again) is so characteristic of a fuel filter that is beginning to plug, but I'm sure that by now you have replaced that. Did you clean your fuel tank when you started on this project? Wish that I could be of more help but you have already done so much!

Jacob AbuKhader

Hahaha your assumption is correct! The fuel filter is brand new. However I did not clean the tank. When I bought it it was my daily driver from day one so dropping the tank didn’t seem really necessary as the car didn’t really have any issues at all.

And trust me I’m greatful for any input on this sucker lol.

Maybe I should just spend 100 grand on a ground up restoration and make this a shops problem. Wouldn’t that be nice 🙄

Spring44

On the early 944's there is an auxiliary air control valve under the intake and once you remove it, it is easy to clean with carb cleaner and test for proper opening and closing. It has a bimetal spring that, once voltage is applied across it, closes off an orfice whose purpose is to provide extra air during initial startup. You can hold this valve up to a light and put a 9v battery across the terminals, then watch as the orfice slowly closes over a 60-90 second time period. Here are two videos on how to do it.

Jacob AbuKhader

Perfect, that’s the part that popped up in my head earlier. As soon as I find some time I’ll give it a shot. Is the other smaller valve for the air conditioning then?

Jacob AbuKhader

Might be on to something with the AAV. I’m not sure if the car is supposed to start with it unplugged but it does.

Second of all the hose attached to it is definitely leaking in air. Not sure if it’s caused my stalls earlier today but definitely an issue that needs to be addressed

Jacob AbuKhader

hey everyone have some info.

I tightened Up the vacuum leak yesterday and all was seemingly well. The car didn’t stall once and I got about another 20 miles out of it

today I went to drive it and this time it finally stalled again.
It lasted 3 miles.

However this time I was armed with both ECUs.

The first time it stalled and wouldn’t restart my original ECU was plugged in. I tried starting it twice and got nada. So I plugged in the other ECU and the car started right up. I then plugged mine back in again and the car also restarted. I drove it home and swapped ECUs entirely so that I could drive the car.

This time with the second ECU same thing, the car stalled after 3 miles. Oddly enough when I plugged my original in, it started right up.

I then plugged the second ECU back in to see if the car would start, and it wouldn’t.

So so then I plugged my original back in and it also wouldn’t start.

Eventually it did restart with my orignal so i babied it home with left foot braking lol.


Theres something worrying me. When the car cranks and doesn’t start, my oil pressure gauge doesn’t go past 2 bars.

When it does start it shoots up to 5 right away.

This happens when either other DME is installed.

I doubt the AAV is the culprit because this tends to only happen when the car is warm and the car does not start then die, it cranks and cranks.

Is my oil pump failing? Or is my oil pressure relief valve failing? Or is the sender itself failing?

I still have Tach bounce and I still have fuel pressure when this happens, the only gauge that’s not happy is my oil pressure gauge

again just now I tried starting the car with the second ECU in and it cranked itself silly and no oil pressure building.

Plugged in my original and it started right up, ran fine for about 30 seconds, and then stalled while it was idling. Just completely came to a halt for no reason.

Jacob AbuKhader

One thing to note also is that any signs of smoking/ flooding have completely vanished. It’s only the stalling issue that’s remaining now. My airbox is as dry as my funds. No oil/ oil residue at all.

Its also interesting to me that my fuel pressure doesn’t drop while cranking. I’d expect at least a dip if they were spraying.

The next things I’m going to try are removing a plug and grounding it to a screwdriver as well as connecting a multimeter to my oil pressure sending unit to verify it’s at least getting power. Unless there’s something else I should be looking at.

Jacob AbuKhader

One more thing to note, I did some searching and it doesn’t seem like I’m losing engine pressure. The car doesn’t suddenly fall to 1 to 2 bars while continuing to run and the oil pressure light doesn’t illuminate while the car is running. I checked the oil the other day and it was a little low but still above the first mark on the dipstick. I then added about 1/4 qt just because it was extra I had laying around.

Spring44

Cranking speed isn't all that fast, so 1-2 bars pressure during this time is of no concern as long as it increases when the engine starts.

Jacob AbuKhader

Okay phew that’s a load off of my mind. I waited a few hours to let the car cool down and ambient temps outside come down as well. With the second ECU installed in the car it still refused to start. But with mine plugged back in it started right away and ran no problems. There is a noticeable difference in how the car runs between the two ECUs. My original one the only issue is the stalling. The other one will sometimes idle all over the place, start and run rough and it 100% stalls the car or fails to start it more often more frequently.

Spring44

Just a hunch, but try tightening the smaller of the two cables on the positive battery post and see if it makes any difference. Last year I was where you are, bringing an '84 back from a long storage and the car would stumble and try to start, but not quite start up and run. I had professionally cleaned the tank, new crank sensors, fuel pump, filters and injectors, had the ECU professionally tested, cleaned all grounds and it should've run but didn't.

I don't know why, but after a long cranking session without it running, I tightened that small positive cable on the battery and the car immediately started, it ran and has run great ever since then. I don't why it worked, it just did. The nut on the cable clamp was not visibly loose, but maybe loose enough to not give a steady voltage to the ECU.

Anyway I pass this along to you in the hopes that your solution might be just as simple and obscure as mine. Good luck, my friend!

peanut

Ahh I wasn't aware that the early 944 had an extra positive supply cable on the positive battery terminal.
That is the permanent direct feed to terminal 30 on the fuse relay board that supplies everything that is not turned on by the ignition switch ie the ECU, DME relay (terminal 30) alternator regulator, lots fuses, lights etc .

That connection is a very important one to keep ultra clean
Good suggestion Spring

Jacob AbuKhader

Hey everyone back with news!

During a no start i measured voltage supply to the injectors and got a reading of 2.5 volts. After about a half hour the car starts normally again and I measure 12 volts at the harness again