altarchsa

I'm losing ground! '89 C4, stock 110k miles

Got the Christmas Tree to stop with 2 new coils. (I also have a new set of wires on the way.) Still working on getting the now intermittent PDAS / ABS warnings completely stopped.

The new coils improved the power dramatically! The car starts good and runs great when cold and at higher rpm's. However, after warming up a few minutes it develops a strong surging when at idle or low rpm. It then starts missing and dies. If I keep the rpm's up (2000+), I don't have a problem. If not it surges and misses, and if rpm's let to fall low enough, it dies. When I crank to restart, it doesn't even try to start for some time (varies). I've noticed a cloud of white "smoke" from the exhaust after a few seconds of cranking, looks and smells like gas vapor from the unburned fuel being pumped through the hot exhaust system. When it finally tries to start, I've noticed depressing the accelerator slowly seems to let it eventually catch hold, then it races off like nothing ever happened. If I catch it when it first begins missing, I can usually race the engine and get it to stop missing and run properly at the higher rpm's.

At first I thought it was losing spark, but then thought it might actually be flooding out.

ISV and MAPF were recently cleaned. Fuel relay replaced. Any ideas???? Anyone????

I've found this to be the most amazing web forum with so many knowledgeable and helpful participants! Thanks in advance for any help.

parsecnc4

It sounds like the O2 sensor may be the culprit, especially when the missing lessens when you are at WOT.

RallyDogRacing

My thoughts do something basic like:
1. ensuring you've got both dizzy rotors spinning (take caps off and have someone crank car)
2. check condition of rotor & cap contacts. Mine were burned beyond recognition - and replacement yielded excellent results w/the new coils.
3. ensure your TPS and Idle Switch are sending good signals
4. check voltage output of 02 as was said above. If no record of replacement - just do it.
5. isn't there a plug under the driver's seat that can force the PCM to bypass the 02 sensor by changing a wire???

altarchsa

O2 sensor was replaced within a few thousand miles. Both distributors working, with aftermarket venting, but caps and rotors probably need replacing. I'll try that with wire replacement soon. Thanks!

I still can't make up my mind whether it's initially an electrical or fuel problem.

BGLeduc

Search in this forum for Airflow Meter Wiring Harness, or words to that affect. There is a TSB that addresses a re-work to the AFM harness that can (in my case DID) cause similar symptoms.

Brian

altarchsa

BGL - Thanks for the advice. Sounds exactly like the problem I'm having. I found the thread for the bulletin and will check for the mod to my connector. That would be too easy a fix, and the kind of thing a novice like me would never find on his own! Will report on results

Henry964

Sorry to hear about your problem, I am a couple of steps behind you, still waiting for the new coils to hopefully solve my christmas tree

altarchsa

I completed the MAF wiring harness modification per the tech bulletin and "VOILA", no more surging and missing on th e30 minute drive in this morning. I'm still holding my breath as one step forward with an old C4 seems to usually result in two steps back.

Many thanks to BGLeduc for pointing out the needle in the haystack!

AndrewM

Also check your fuel pressure, sounds like the symptoms that a friend of mines C2 had. Went through everything on that motor and the fuel pressure regulator was bad. GL
Drew
86 930 (still at IA)
89 C4 (gone, not forgotten)
97 C4S(gone, not forgotten)

BGLeduc

Good luck...hopefully that will be a good fix.

As you probably can tell from this thread, there can be problems with similar symptoms that may have very different solutions. That's all part of the ownership experience, I suppose.

Brian

altarchsa

Andrew,

I drove it around downtown today in 75 degree weather and experienced only one period of problems, similar to those described. But it is much, much better. It may be a combination of things and the fuel pressure regulator could also be a problem. I may try to check that if I have any more problems, but right now its 95% better on this issue.

Thanks!

Twood

This sounds very much like my problems. My O2 sensor was only about 18 months old but changing it completely cured my car's problem.

https://rennlist.com/forums/showthre...ighlight=twood