EckFe1

97 993 C2 Cab, bought the car with worn belts, no CEL, didn't change them til the alternator went in a big way. It even turned the AC belt to running inside on the outside. Wasn't prepared for that so I called roadside assistance. To be able to drive the car home, they installed a much wider Ford belt and used a fender washer from a guard rail for the upper pulley. I drove over 200 miles with it, no CEL. Once home, I changed all belts with OEM parts. I didn't like the way the alternator belt fit around the top pulley. It looked way too short but I drove it for 2 months. Anyway, I purchased a longer aftermarket Continental belt which is 10mm longer and not 9.5 but 10mm wide. It now runs nicely almost even with the top of the pulley edge. Had that in there now for another 3 months with lot's of spirited Autobahn driving. No CEL yet. Noticed that the belts have a bit more slack now then when I installed it. I might take a washer out to compensate but sofar they all run great.
I have a hard time understanding all your belt problems.

swmic

Wow nice find!

How was the bad belt causing the misfires? Was it causing a low voltage condition or was it slipping, kind of - on and off, causing noise in the electronics?

cabrio993

Been there, done that.

https://rennlist.com/forums/993-foru...light=oem+belt

https://rennlist.com/forums/993-foru...light=oem+belt

Always use OEM belts (good ones) . Stay away from Continental and others.

Glad you found the problem.

Mark Harris

Bravo. Too bad more people don't drive their 993's the way they were designed to be driven.

Fly911

Concidering where he is coming from, Tony Callas has to be good, very good indeed. I have been using Rennsport Porsche Works in Sealy, Texas (one hour drive west of Houston) for all my Porsches, where Tony's father Mike Callas has been running the shop for nearly three decades. Mike is probably one of the best (if not THE best) air cooled Porsche mechanics in the US. I can highly recomend Rennsport and Mike Callas to all Houston Porsche owners!

Martin S.

Tony does an annual 993 seminar that is incredible. I have missed the past few because of scheduling conflicts, sad to report. THis guy really knows the 993 cars.

Kika

Glad to hear it worked out for you!

Tony is a class act!

Stuttgarter

Um, aren't you forgetting the collapsed vacuum hose that Tony also found and replaced? I was assuming that had more to do with the CEL than the belt.

PNogC2S

Nope! The belts are definitely a culprit with CEL - and it will generate a bunch of random misfire codes on the OBDII . This exact same thing happened to me about two years ago. I replaced the belts as part of a service and used some that WorldPac said were "OEM", but they didn't have the Porsche logo on them. It started generating misfire codes. I took it to several very respected places in the Bay Area, since I was stumped... was told the problem could be the fuel injectors, bad flywheel, etc... Well, a very smart guy at PCA said "just change the belts!"... it didn't make any sense since I had new "OEM" belts, but it was the cheapest option, so I changed them for belts I bought at the dealer. Voila, CEL and misfire codes gone! I'm only buying dealer supplied belts for the 993 from now on.

Lorenfb

"Always use OEM belts (good ones) . Stay away from Continental and others."

That's the key! Most/all good Porsche shops have known this for some time now.
The problem is related to the different RPMs between the alternator and fan
unique to the 964/993, but not problematic for the 964 as it lacks misfire
detection in its DME ECM.

IXLR8

Alternator belt slippage?

How exactly does that cause an engine to misfire?

Amfab

It doesn't. It is my understanding that the slipping belt causes slight variations in the crank speed that in turn causes the sensor at the flywheel to be misinterpreted by the computer as a misfire...

at least I think that is what is going on

IXLR8

There are crank speed variations at idle. Somehow I doubt it.

Now if slippage was so great to have the battery slowly deplete, I can see the CPU not functioning properly. But that much slippage would generate heat in the belt and rapid failure of it.

I'm still

Maybe the reason wasn't conveyed accurately.

JasonAndreas

Try THIS explanation.

cabrio993

That is correct!