Jerry Garwick

Does the check engine light come on at a certain interval (every so many miles) or only when a "glitch" is encountered?

springer3

I have read the documentation in the factory manual, and I don't recall any periodic schedule for the light. I think it means that a problem has been detected.

Lorenfb

The CEL (check engine light) should come on when the key is in the run position
and go out once the engine starts. It will only remain on if there's a problem related
to the engine's fuel/ignition management system. Many 964s came to the U.S. without
the bulb installed. It's a good idea to install the bulb if the car lacks one, as this will
provide the driver an indication of any engine problems.

jrb964

Jerry - I've just resolved this problem. My check engine lite was coming on and off with no apparent pattern. It was really frustrating. Took it to my mechanic, and he checked the code and it was a knock sensor. Searched Rennlist and determined that the connectors on the top of the shroud just needed to be cleaned. Used some canned air and brake kleen. Cleared the problem up.

Hope this helps.

Jerry Garwick

Knock sensor, here I come! Thanks for the tip.

Bill Wagner

Jerry:

Just because someone else had a fault that they corrected by cleaning their knock sensors doesn't mean that's what the problem is. Go to my web site (sad looking, but I intend to update it soon) and I have a write up on using the CEL. Note that the CEL doesn't work on all cars, just those I've identified. Often it IS something trivial, like a loose wire or dirty connection, but without knowing the exact source, you might just be wasting your time. If your CEL doesn't work, you'll need to take it to a shop and get the fault read with the hammer.

Good Luck

Claude

Bill: Thanks for the info on CEL. I do get the intermittent CEL but I get faults code 1500. This happened with greater frequency when I bypassed the secondary muffler but NOT when I bypassed the cat. I do have an O2 sensor on my cat bypass. The CEL only comes on 10-15 seconds after hard acceleration. Any ideas?

Lorenfb

You really need to drive with the Porsche Hammer hooked-up to immediately
read the fault codes. The fault after hard accel could be:

1. an overly rich fuel mixture the result of a mis-adjusted air flow meter
2. a bad performance chip
3. ignition system wiring breakdown (high voltage breakdown causing noise
input to the DME), a common problem
4. a bad fuel pressure regulator allowing too much pressure when intake vacuum
drops for enrichment on accel
5. a broken belt in the distributor

John Speake

Fault code 1500 actually means "no faults stored"

Bill Wagner

As Lorenfb indirectly points out, the CEL system is NOT the be-all end-all in diagnostics. It only detects and stores info related to SOME components (primarilly emission related, but obviously performance related as well). I should probably update my web page to reflect this.

CHEERS!!!