chili964

Need some help 964ers. My check engine light came on the other night as I hit the accelerator to pass up a snail driver. When I got home I disconnected the battery, reset. The engine light stayed off until I again hit the accelerator (4500+rpm). I pulled over, disconnected the battery, reset. I have kept the rpms under 4500 and the check engine light has not come. Any ideas?

J.PELLEGRINO

I would find a qualified shop or a friend with a hammer or pst2 and have the system checked.If the light is on,the system has a recorded fault and it should be pretty easy to diagnose.My first suspision would be involving the resonance flap and its associated componants.I have see this and it is active around the rpm you seem to be fllging the fault.It could be a electrical connection or perhaps a vaccum problem.Their is a vacuum resivior under the intake and a electromagnetic switch that controld the flap dashpot.Good luck,but that is where I would start.

91C2wrencher

do a search under "fault codes" for some possible help

mark964

This sounds like a "faulty" knock sensor. I had this happen in my 91 C2 Cab. The symptom ? Period illumination of the check engine light under load. All I did was disconnect the two connectors and clean the contacts. Problem solved.

FYI, the knock sensors are the two 3 pin green connectors in your engine bay. The sensor for 1-2-3 is located on the back left of the engine attached to a bracket on the intake. 4-5-6 is located on the top of the intake.

If you have a U.S. car you should be able to read out the emissions related fault codes yourself. I have the procedure if you need it. I believe the codes are 1231 for 1-2-3 and 1232 for 4-5-6.

Mark

Adrian

Seeing something happens at approx 4,500 - 5000 rpm (indicated) I would suspect your reasonacne valve has failed. This is a solenoid operated vacuum valve which opens and extends the length of the air intake. The DME monitors the solenoid. It may not be activating.
The other possibility is that the WOT (wide open throttle) microswitch is not working and the DME is seeing it as failed when it wants to switch to "full throttle mode" at around 4500 rpm.
Quite a lot happens at around this engine speed.
Ciao,
Adrian
964C4

Lorenfb

Now is the time to check the fault codes using the Hammer or
the ST2. You can also readout the codes using the CEL. It's best
not to guess at the problem unless you have a lot of free time
to troubleshoot or extra money to buy parts.

Have Fun
Loren

Adrian

If you are a DIY sort of person I would advise some self troubleshooting and learning. I do not believe in putting money in others pockets unless you have no mechanical or technical skills or you have no choice.
Can be a lot of fun doing some of this yourself. The check engine light can be used to read out the fault codes. Give this a go and see if you can decode the flashes. Bill Wagner has done some work on this on his web site. Check it out.
I am helping a guy out in Asia right now who has had his car (before he found our group) checked with a Bosch Hammer and the mechanics replaced every component that threw up a fault code. His bill is enormous already and the problem is not solved and now they are trying to sell him a new DME.
Ciao,
Adrian
964C4

GMS

I'm sorry Adrian, but people who replace parts in the hope of solving the problem are not "mechanics" they are parts changers. I would also suspect that if the shop is in a part of the world where Porsche is not common there may be a lack of product knowledge. Mind you, that also occurs in other places where Porsche is a more everyday car. A lot of this is happening because the structure of the motor industry is changing; technicians are aging and there are fewer recruits to replace them, and many of the brightest ones go to the dealers where they rarely see older (out-of-warranty age) cars. Technicians with good basic diagnosis skills and common sense are just getting older and retiring, or moving out of the trade.