964 C2 runability problem

[kiesan]

Hi guys. Attached below is my text for a 964 problem I posted over on Rennlist. I've gotten some good suggestions over there but I thought I'd put it up here as well. Sorry its so long. Any ideas or suggestions please let them fly~





My '92 C2 has 60k on the clock. All stock engine and exhaust, I bought it 4 months ago at 54k and it has always ran like a clock until just recently. A very well maintained car it is.

The rear window got broken out a month ago and the car sat in my shop for 10 days or so waiting for the new glass. I drove it to the glass shop and they installed the new glass. I picked it up that night and immediately it didn't like to start cold or idle either. Also, engine check light on. I drove around the city a bit and suddenly it seeemed better, but still the check light would stay on at times after starting and eventually go off. The car had never acted like that before in my ownership.

I went to my favorite Seattle shop, Gerber, and we all came to the conclusion that the battery went flat while waiting for new glass and it just hadn't fully charged. I charged the battery and all seemed well for about 10 days and the same symptoms returned.

Back to Gerber and this time it was for sure the alternator was toast. New alternator and battery just for grins and car runs way better for sure. Cranks faster, heater fan faster, etc.

However~

I still get the check light about half the time when starting the engine. When it goes on, it stays on for maybe 30-45 seconds and usually the idle is pretty rough and will die when you come to a stop. Also, the idle seems to surge or fluctuate more than I remember when I bought the car even when the check light is not illuminated.

The tech at Gerber is a good friend so we have made arrangements to swap cars and he is going to have it for as long as they need. I have the 911 Enthusiasts Companion and the troubleshooting area has quite a few things to check for idle problems although I'm not seeing a section for the engine check light.

Thus far, the car has a new alternator, battery, ground strap, O2 sensor, idle air control valve, caps & rotors, spark plugs, dist belt. Also checked the valve clearance and changed the oil just for grins. Reset the computer with the 'hammer tool a bazillion times.

The darn thing runs like new, EXCEPT, the check light still comes on at times right at startup. Normally goes out after 30-45 seconds although sometimes it won't. When the light is on, the car usually will just barely idle or not idle at all with the tach jumping up and down. One time we got it to happen with the 'hammer hooked up and it showed nothing strange other than the computer trying to compensate (advance) the ignition timing while the engine was going ballistic.

Gerber Motorsport now has the car for the duration to get this licked. I'm pretty sure they are going to try the tried and true parts swap/process of elimination with the spare complete 3.6 motor and such they have lying around.

Another symptom that very rarely happens is excessive cranking when starting the engine after it is warm. As I said this is really rare and I'm guessing is unrelated but the more info the better.

Anyone know what sort of paramaters or conditions need to happen to make the light stay on? I've noticed it is supposed to come on when you turn the key "on". The split second you start cranking, the light should go off. What exactly is that light an indication of?

I'll even put some Ferrari bashing in here. Since Gerber has the car, I pulled my 328GTB out of hibernation. What a turd! At least when compared to the 964. Rides like a truck, wallows around, no power steering, etc. Still looks and sounds pretty good, though. I guess the fact that I never drive the thing after getting the 964 says it all.

Still looking for suggestions if anyone has some. We just plugged in a known good RS America ECU and so far no problems but we'll see... I'm not convinced.

[Don Settergren]

The check engine light is always associated with an engine managment code. You can read the code using instructions you'll find posted on both Pelican and Rennlist or your mechanic can read them as well. The code will help us DIY-ers a great deal...

[kiesan]

Originally posted by Don Settergren
The check engine light is always associated with an engine managment code. You can read the code using instructions you'll find posted on both Pelican and Rennlist or your mechanic can read them as well. The code will help us DIY-ers a great deal...

Thanks Don.

Well, with guarded optimism I think the problem is fixed. Last Friday and Saturday it was getting much worse. We swapped in a known good RSA ECU and after driving the car a lot since then, on and off numerous times, no signs of the previous symptoms.

This problem never triggered a code when checking with the hammer so this was a shot in the dark.

Keeping fingers crossed.

[Don Settergren]

Cool! Did you notice any additional power from the RSA chip?

[kiesan]

Originally posted by Don Settergren
Cool! Did you notice any additional power from the RSA chip?

Well, thats a good question. From what I can tell, RSA's have the exact same ECU as my '92 C2. The part numbers on the units were identical.

However, this RSA ECU had clearly been opened before. The RSA it came out of was a low-miler (16k) that had seen plenty of track time, it was actually wadded at the track. The car had big wheels, suspension, harness bar, etc. A likely candidate for some kind of upgraded chip if there ever was one.

The tech who drove my car for a couple days kind of smirks and says he never would drive my car in such a way as to determine whether or not it was chipped. Yeah right!

To me, it seemed healthier and maybe a little noisier at WFO but I couldn't be sure. I'm going to ask the former owner of the RSA to be certain.

[Tall02]

Dear K

It sounds like your engine idle was hunting (modulating up and down). And possibly when the RPMs are low the alternator was generating low voltage causing the alt light to stay on.

I too have a 92 Porsche 964 and it idles a little rough like it has an oversized cam. Not sure if it is stock or after market. But I am not encountering any alternator light staying on. I am interested in hearing if the ecu solves the problem.

Good luck

K

[kiesan]

Originally posted by Tall02
Dear K

It sounds like your engine idle was hunting (modulating up and down). And possibly when the RPMs are low the alternator was generating low voltage causing the alt light to stay on.

I too have a 92 Porsche 964 and it idles a little rough like it has an oversized cam. Not sure if it is stock or after market. But I am not encountering any alternator light staying on. I am interested in hearing if the ecu solves the problem.

Good luck

K

Thanks K.

Well, my alternator light never came on during any of this. The engine check light is what was coming on for me. We replaced the alternator simply because it was putting out a little low and we wanted to eliminate that possibility.

Since the ECU change, no engine check light so I'm thinking we got it.

K

[kristian85]

Kie, you have PM.

[kiesan]

Originally posted by kristian85
Kie, you have PM.

Kristian my PM box is empty but I did get an email from you yesterday and I replied last night. Ring me up if need be.

[tshih]

My 1993 C2 had a similar problem at 10K miles. It turned out to be a defective intermittent problem with the AFS ($500 to replace yourself). The Hammer was bought and it gave that code as well as the ubiquitous O2 sensor code each time it stalled and ran poorly. There is no difference between the RSA and C2 except in suspension and weight and optional deletions of equipment and upgraded wheels and tires. No change in power and chip ECU.

[DustinTarditi]

Kie,

Looks like you found the culprit - If you haven't yet, also get a spare DME relay...

I did enjoy the comparo to the 328, BTW. A fellow PCA buddy always pines about how he wants a Ferrari yadda yadda... :-)