Strange Intermitant Stalling Problem when engine Hot -Not FPR or Crank Sensor related

[toolman2005]

Im hoping someone out there maybe able to shed some light and help diagnose a strange stalling problem on my '97 Aurora.

The problem is NOT related to the Fuel Pressure Regulator or Crankcase Sensors, as is the typical problem I have read about. I have actually replaced these parts hoping it would fix things, but the problem still keeping coming back. There is never any check engine warning lights.

The Problem started last summer and went away when the weather got cooler. Not a single problem until around late March. It will stall while driving or when stopping, usually more likely if caught in heavy stop start traffic. If I manage to get on the highway and get a good run it seems to recover and be ok, but once off the highway it can start stalling again intermitantly. The car will restart if you let it sit for 5-10 minutes.

The stalling only happens under specific conditions:

-The car has to be driven for sometime, like 45 min +. Usually having stopped and parked somewhere for a while, then dring somewhere else.
- The Engine Temp is usualy just above the 95' C range, but it has happen when slightly cooler. but still around '95 'ish.
-Seems Outside temp must be 12' C and above. Never happens when cooler.
-It apears that it hjas something to do with the continuous driving and heating up the engine bay area for some time.

I have had several diagnostics done by GM and another service centre, and no one can find the problem. There are NO engine warning lights or codes EVER. I have had the fuel filer replaced and thr throttle boy cleaned etc. too.

I have also swapped over the Fuel Pump relays in case that was the problem, but it didnt help.

I am starting to think that it maybe PCM or fuel pump related, as the problem does aprear to be fuel delivery. I read on another post here aout someone with starting problems and they had replaced the fuel pump, but the problem came back. I think It might have been a fuel pump in the end. But one person had mentioned a service diagnostic procedure to check if the PCM is sending a signal to the pump relay and if there is a problem there by feeding 12v directly into the circuit (removing the relay first). I have tried this but the car still had a problem starting. I noticed shortly afterward when it did start that you could hear the pump prime. This WAS NOT HAPPENING when trying to restart. It seems that when it does restart, that the pump primes at the same time.

I think that it 'might' be then either the PCM not sending the signal to prime the pump, or it is a problem with the fuel pump itself.
However, I would think that if it was the fuel pump though I would have the problem in the winter too???


This car has been fine until this started, and its a gremlin problem that no one can seem to isolate.

thoughts and help from anyone out there please!!!!!!

[tjm]

I would agree that the problem is fuel delivery - fuel delivery issues are one of the only things that will not set the SES light.

So let me ask you - does your gas gauge work? I fit doesn't or acts up from time to time then it's a good excuse to do the pump.

I had a very sim prob with a different car but never nailed down weather conditions and such. I did the fuel pump - no change. I took it to "the best place in the city", they replaced the coil pack and it was fixed. Go figure.

I am still leaning toward fuel pump for your issue - I did mine at 130k miles I think.

[tjm]

one other thing - check all vac lines and intake manifold bolts too - vac leack can cause those symptoms too.

[toolman2005]

Thanks Tim.

My car has done around 185,000 Km. So I'm guessing its the original fuel pump.

I have never had any problems with the fuel guage, which is why its a little confusing when you think that it never happens in cooler weather (below 12'c). I would still expect a fuel pump to have the problems in the cold too. But maybe im wrong.

I have tested for spark when the engine will not restart, and it seams the ignition is ok.

Just as another note, I can drive for hours on a long highway trip, and will never experience the problem. Only once I start to get into stop/start driving in heavy traffic.

[tjm]

185000 km/115,000mi almost seems too soon for a fuel pump but who knows. We don't know how many hours it has on it do we. Your 115000 miles, if city, could be equal in time to the 130000 miles of highway when I had to do mine; although mine was mainly for the gauge.

So what else - catalytic converters might cause this too I think; smell any rotten eggs lately?

Sticky EGR system would not cause the problem on the highway but would have issues coming to a stop with rough idle.

The coil pack I had replace showed "intermitant" problems.

Check this forum:
http://aurorah.proboards47.com/ and post this issue in the "Classics Mechanical" area. There is another post with a similar issue we have been trying to work out. Keep your issue in a separate thread though.