Misfire and CEL cleared w/ Porsche Belts

[hkate]

As my first post EVER, I want to start out by thanking everyone here at Rennlist (and PCA) for their forum contributions. Without you, I would never have figured this out.

The setup: Bought '98 993 Cab in Jan '07 w/ 95k miles. Previous owner neglected 90k service (plugs, belts, fluids, filters, etc) so I negotiated the cost out of the purchase price. Mar '07 I took the car in to my indie Porsche mechanic and when I got my baby back the dredded CEL light came on -- misfire codes 303 and 306 (cyl 3 & 6). My mechanic tried everything -- new plugs, wires, rotors, caps, nothing helped. They even dropped the engine and looked at the flywheel and sensor, compression check, injector check, you name it. This is a very reputable shop in So Cal and didn't charge me a dime. I took it to the dealer who quickly diagnosed a topend at $10k! Doubtful as this didn't seem to be a SAI problem. Couldn't be a hidden previous owner problem because I had a PPI done.

Fast forward to Dec, (not really, that CEL bulb is very annoying I finally had to take it out) searching the posts, where I read it might be the belts. Could it be that simply? Bad alternator and fan belts? My mechanic thought it was highly improbably as they've used Continental since 1990. But what the heck, give it a go, and replaced the Continental belts with Porsche factory belts.

Success! CEL is out and hasn't come back. No codes what so ever!

Again, many many thanks to everyone on Rennlist!!! Happy New Year!

[chris walrod]

Welcome to Rennlist! Congrats on your purchase and getting this issue behind you.

Tony Callas was one to share his vast knowledge on the misfire subject. He shed light on misfires being a result of loose DMF and loose/poor condition belts. Two areas many folks overlook when troubleshooting a misfire problem. Strange indeed, but it seems these theories are real.

[goofballdeluxe]

Hey there and welcome to Rennlist! Glad to hear your problem was worked out. Since I too am in Southern California, I'd love to know which reputable shop you took it to that did all this work without charging you a dime. If you'd rather not post it, please send me a private message if you would be so kind. Enjoy your 993 and thanks in advance!

[Mike J]

Interesting and something to note....it must be the little German elves inside the engine being picky about the maintenance schedule...

Cheers,

Mike

[autosea]

I know exactly how you feel and what you went through. I to have a 97 993 and the CEL light had been comming on since I got the car(about one year).I asked my friend who I got the car from and he said the light is always on , No big deal. My car has only 28,000 miles and I had read about the dreaded valve guides, top end rebuild, etc.
I took the car for the 30K service and found out the CEL was due to a missfire and they cleared the system. Later the light came on. I was going to make an appointment at the same time was reading on Rennlist and heard about the belts and decided to replace the belts. Well knock on Porsche the light has not come on since.
One thing in life makes me so happy and since I never had the chance to graduate from highschool is the fact that if you want to learn there is a way. The information is out there.

[hkate]

My mechanic and I have yet to fully understand why the non-Porsche belts caused the misfire. As I said, it was a first for them. I know there are lots of theories out there -- loose fly wheel, static electricity, bad belt tension, etc. Is there a definitive answer out there?

[kevin993]

You never know who you'll see pop up on Rennlist... Enjoyed running with you and meeting you on the New Years run. Loved your other p-car. Thanks much for sharing the info. Look forward to seeing you on the next run...

[hkate]

Will we meet again at POC later this month?

[jimbo3]

Originally Posted by hkate

My mechanic and I have yet to fully understand why the non-Porsche belts caused the misfire. As I said, it was a first for them. I know there are lots of theories out there -- loose fly wheel, static electricity, bad belt tension, etc. Is there a definitive answer out there?

I understand it to be that the crank position sensor can't get a good reading if the belt is a little too loose due to a vibration and/or oscillation that sets up.

[mbriggs993]

I had this same issue shortly after my 30,000 mile service about three years ago. Took some time to diagnos but once the belts were changed the light went away and has not come back. It was a great relief.

[Amfab]

Same problem here and the belts fixed it, supposedly the minute slippage of a worn or non-factory belt give the crank snsor the same stumble as a small misfire

[SPDYELW]

Originally Posted by jimbo3

I understand it to be that the crank position sensor can't get a good reading if the belt is a little too loose due to a vibration and/or oscillation that sets up.

BINGO!

Congrats and welcome. I had a similar experienced with my '97 C4S (58k miles). Did every possible things (except for dropping the engine). Then my mechanic called his porsche master tech and suggested to replace the conti belts with porsche belts...voila!

Reason being....as stated above.

[geolab]

and that is why I bought this some time ago

[hkate]

Great news - I just passed CA smog with flying colors. No MIL or CEL issues. It's been 2 months and 150 miles since I swapped out the belts. This 993's emissions systems are working great. (Actual tailpipe tests register virtually no emissions what so ever.) Hard to believe a non OEM belt could cause me so much grief. But I'm glad it's over, at least for another 2 years. Oh, and by the way, my car has 96k miles and has never had a topend or SAI issue. (knock on wood!)

[Avenger6]

Geolab -

What did the belt tension tester doohicky cost?