New Guy!!

Freaky · 08:43 PM

Hi, I'm new to this forum and to Porsche and I have a problem. This morning pulling into traffic I went into boost, hit the rev limiter and then the engine started running rough and I had a couple of backfires....shut the engine off, and now it won't start.

We pulled the belt covers, and know that the engine did not jump time nor break a belt. I have 39psi of fuel pressure, have tried 2 different DME's, DME relays, have bypassed the factory alarm, and tried 2 different AFM's.

The car turns over just fine, but there is no spark...oh, we have also tried a couple of different coils. Grounds have all been cleaned, and reference and speed sensors have been replaced (I have two friends with the same year 951's helping me...So I get to try their good parts). There is no cycling valve, as the car has a tial dual port wastegate, kokeln turbo, and a vitesse maf.

As I said, everything appears fine, just NO SPARK! I did see one post where the guy found his ISV was bad, causing the car not to start, what's an ISV?

The car is a 1987 turbo.

Thanks

rick13 · rick13's Garage

does the tachometer bounce when you crank?

Freaky · 01-14-2014, 08:43 PM

one bounce when I first turn on the key...no bounceing when cranking...we adjust the sensor bracket to the factory distance, and tried different sensors (removed from a running car)

Freaky · 01-14-2014, 10:44 PM

What is the ISV?

sketchers356 · 01-14-2014, 11:38 PM

ISV = idle stabilization valve???

rick13 · rick13's Garage

No bouncy...no good. Hmmm...maybe the set screw for the rotor came loose...? That happened to me once.

kdjones2000 · kdjones2000's Garage

That or your DME died. I had that happen to me, for no particular reason. Having no tach bounce during cranking indicates you are not getting your injectors to pulse. Also check out your Speed/Reference sensor connections, and ohm them out. Look at the Clark's Garage No-Start suggestions.

You over-revved the car, so it should have gone into "limp mode", where it would barely run. Normally you turn the key off and start the car and it comes back.

It sounds like the computer never came back, or could be the KLR. You can jump out the KLR box and see if the car runs. The DME would require you to swap in a known good unit, or send yours out for testing.

Good luck, Keith

Freaky · 01-16-2014, 08:48 PM

Thanks for the post Keith

I tried a known good DME, no luck, replaced the speed and reference sensors with known good, and reset the gap also...no luck. Will try the KLR next. I just put a test light to the injectors, and I have no pulse, could this also be caused by a bad ignition switch?

kdjones2000 · kdjones2000's Garage

Look for "DME Test Plan" and you should find a very nice flow chart on what to diagnose. I would jump out the KLR and see if it runs or not.

Your alarm can also take out (I believe) spark and injector pulse, but be careful following Clarks or others on how to jumper that out - it can lead to shorts/fires on the later cars - '88 and up I believe.

Freaky · 01-17-2014, 05:37 AM

Alarm was bridged with what looks like a factory plug, it's non-existant, I checked the injectors with a DVOM, and show 12v on both terminals, Clarks Garage says one terminal should register 12v and one should 0v. Any ideas why I would show 12v on both terminals?

Where would I find the DME Test Plan? How do I jump out the KLR?