2002M3Drew

Strange problem I'm having on my 911SC!

Here's the full story...I was away for a week, and hadn't driven the Porsche for a good 10 days. When I went to drive it, it really fired badly, sounding like it was on 5 cylinders, stumbled a bit, and died. I cranked it a couple of more times, and every time the same result. On the fourth and final try, it starts right up, goes to the correct idle speed, and all is fine. I drove it several times during the week with zero issues.

I decided to take it to an autocross yesterday as a warm up for a two day DE next weekend. All was fine again for the first two runs. I shut the car off after the second run (not after the first), and when I started it back up, it didn't seem like it was running on all cylinders...not as bad as earlier in the week where it would die, but it was missing. I did my run and confirmed my suspicion...absolutely no power. In the pits, a mechanic friend (though not Porsche mechanic) played the spark plug wires and we removed the distributor cap to have a look...all looked fine...looks new, in fact. I crank it and it's back to normal. I do my next run and it's back to 100%. In the afternoon, I fire it back up to start my afternoon run group and again, it's fine...at 100%. I set my own fastest time on that run. I thought about keeping it running between runs, but then decided against it because of the length of time, and shut it down. I go to start it again and the problem is back...bad missing. I decide that that's it for the day...I don't want to risk breaking the car. We continued to play with it throughout the afternoon, but it never got any better. In fact, as it cooled and we fiddled and would restart it, it got worse and worse. We thought for sure it was one plug wire, but now more than one cylinder seems to be affected. By the time the tow truck came, it wouldn't stay running for more than a second or two.

The battery seems fine...it cranks strongly. the motor itself seems good, because as I said, when the problem decided to go, the motor was absolutely perfect. I'm thinking it must be an electical issue. Earlier when it was missing, we could hear clicking on the left side, like arching...that led one person to suggest it was one spark wire.

Any ideas, guys??

DGaunt

Bad connection at t he coil wire, col connections, plug @ CD unit? vould be a few things, but sounds like ignition for sure. I'd look for something getting loose when hot.

emcon5

My 82 had similar symptoms when the Permatune CDI was on it's way out. Sometimes it would run great, sometimes it would barely start and run like crap.

It was hard to track down, because it passed the bench tests on Permatune's web page, but failed intermittently under load. I replaced it with a rebuilt Bosch, and the problem went away.

Tom

2002M3Drew

Thanks for the replies!

It gets weirder...

I go down to where the car is parked to get it towed to the shop, and just for grins, I try to start it. A few failed tries, and a period of some rough idling, and all of a sudden it starts into a perfect idle. I drove it around the parking lot, went to go fill it with gas, and no problems. So, just to be safe before hitting the road, I let it sit for a while running, and sure enough, the problem resurfaced.

It also ran roughly, and then perfectly after getting it off the flatbed! Stange! It seems to have a fuel mixture problem when stone cold, and then an electrical problem when warm. I'm hoping my wrench has a good idea!

2002M3Drew

And the verdict is....a fuel pump relay! Also replaced the iginition wires, though, just to be safe...connectors were way too soft from age. Seems to run fine now...we'll see!