1500 FI stalls during warm up phase

Mxgrds

Mxgrds

True Classic
Some month ago my FI 1500 from 1981 started to stall when stopping for a crossing during the first 10 minutes driving. Checked and replaced already many things, but nothing seems to help. The cold start is fine. It starts almost instantly and then runs fine for 60 seconds. Then the idle starts to lower 500 rpm. When decellerating the engine stalls immidiately.

Aav- replaced and works
Grounds -checked and repaired
Tps - clicks when throttle is operated
Coolant temperature meter - works, readings are according specs
O2. Sensor - replaced
Checks for air leaks with smoke - no air leaks
Repaired some connectors in the wiring of the injection harnass.
Injectors - checked, nice spray
Afm - checked and works

When the car is on temperature it runs smoothly and idles fine.

Question: during the warming up phase is itonly the aav that should take care for the additional idle or is the ecu also signaling to the injectors to spray more often ( based on the coolant temperature sensor readings)?

Read all of the idle posts on this form, but still no answer yet.
 
Temp Sensor II...

Ohm test your Temp Sensor II.

To answer your question, the AAV provides extra air, but more fuel is needed which the AFM flap measures out, according to the mixture for the temperature, provided for the Temp Sensor II.

If the Temp Sensor II isn't within spec, it could cause this.
 
I know the ljetronic diagnotics manuel and have checked all these points. However where is the tempsensor II located? Did I miss that one?
 
The coolant temp sensor looks okay. Readings are okay. There is not a hidden second (II) temp sensor?
 
There is another temp sensor, Temp Sensor I, which is inside the AFM. It hardly ever (never) is a problem.
 
Ah, the air temp sensor. Readings are also okay. Could it be the ecu? The ecu is just not giving more fuel during warming up? Seems strange as anything else works fine.
 
FPR?

Have you checked the fuel pressure regulator for a vacuum leak?

Also, back to basics, how old is the filter?
 
No air leaks. The fuel filter is replaced this year. Also when warmed up, there are no problems anymore. I assume that it is not getting the extra fuel during warming up to give it a bit higher idle.
 
I have my idle up a little higher on my '81, dash tach says something like 1500 but it's a liar, I just go by ear. Where does it idle when warm? My double relay would start clicking until I bumped the idle up a tad. Maybe bump up your idle a freckle?
 
When warm it idles at 900rpm. That's were I adjust it on. Have not checked it with another tach meter than the one on the dash. Maybe i will do that first.
 
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Sounds more like the AAV is closing too quickly.

Give us a sample of your RPMS at various stages of the warm up period. For example what is your RPM at first fire and each minute afterwards until fully warmed up?
 
I have a switch to delay the AAV to close. As a manual choke. Helps a bit, but not enough.
Directly after starting the RPM is 1000 for a minute. I assume that's on the cold start valve injection. After that it drops slowly to 400 RPM. The engine stays running, although with a rough slow idle. When giving some throttle and suddely stopping, it will immidiately halt. As if the idle swings far below 400 RPM causing the double relay to release.
 
I would set the idle up a little and see how it behaves.
So you wired in a switch to break the circuit to the AAV? Disabling the "heater"? It will close pretty quickly anyway as it's mounted to the head so engine heat alone will close it off, not sure how much difference there would be between the powered heater closing it vs. the ambient engine heat. Those things are slightly adjustable too. There's a nut you can loosen, tweak the plate and re-tighten, I've not done it but I have played with some AAVs a little (sound like you have too).
 
How long the cold start valve (CSV) operates is determined by the thermotime (TTS) switch, which of course measures coolant temps.

At the coldest temps, the TTS will activate the CSV for a maximum of 8 seconds per starting cycle. The TTS has its own internal heating element that heats the switch when the ignition is on, which helps to prevent too much fuel from flooding the engine after repeated starting attempts. Once the TTS is at about 95 degrees F, it no longer activates the CSV. So, over the course of say four or five starting attempts, the CSV would be activating less and less and then eventually stop.

So your thought about the car running on the CSV for up to a minute is not correct.

Can you explain how you have the auxiliary air valve on a switch to delay closing? The only way I would think that would work is if your switch keeps the electrical circuit to the AAV open, which would prevent electricity from getting to the heating element inside the AAV and slow down its rate of closing.
 
AFM

I had similar issues with my 1.5. All electronics checked out per the Bosch bible. My afm was 100% to spec. Car would start; idle for a 10-30 seconds then die. Did the fuel system ect... No improvements. Found the AFM went haywire with engine vibrations. Opened the AfM cover and found a crack at the base of the "tongue". Never could replicate the issue even when shaking it by hand. Replaced AFM and problem went away.
 
Thanks for all your thoughts on this issue, reaaly appreciate it.

The aav closes on electricity in 5 to 6 minutes. Checked that with a usb microcam. The aav is not attached to the cylinderhead anymore, a broken bolt. It is now on a bolt on the camshaft housing. That place takes longer to get warm. So i am sure it is the electricity that closes the aav. The switch prevents the heating element in the aav to warm up. For clarity, i had this problem already before the aav was on a different place. The bolt broke in the search for the cause of this problem.

The afm seams to work okay, at least when the engine is warm.

Although the cold start injector only works for a few seconds to start the engine, i have the impression the fuel injected last a bit longer to keep the idle higher. The whole metal housing is filled with a mixture of fuel and oxygen that will keep the air/fuel mixture for a certain period (longer than the 8) seconds richer.

Somewhere along the way I have exchanged the motor oil with 20w50 for classic cars. Could the thickness of this oil, when cold, give enough resistance to slow down the rpm? There is only a little bit more air needed to keep it running. The aav should open up a bit more when cold.
 
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Just an FYI

Comparing against a very high quality automotive multimeter, I have found that the tach on my '86 FI car reads about 1025-1050 RPM when the meter says 900.
 
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