DME Relay Ground Activation Signal

[PowerHaus944Turbo]

All,

My DME relay seems to be cutting out for half a second every so often and I traced the problem to the ground activation signal (from pin 20 on the DME). I tried swapping out the DME, but it didn't solve the problem. Does anyone know what sensor or input might be responsible for this?

Thanks,

Will
1987 951

[PorscheG96]

How did you track the problem to that pin on the DME?

I'm not sure where the ground for that pin can be found but obviously that's what you need to look for. Cleaning up the ground [it's probably all corroded] should do the trick.

[PowerHaus944Turbo]

My initial post was a little vague and incomplete. I am currently using the Porsche DME/KLR test plan (WKD 453 920) for most of my information.

Here is the symptom:
- At idle, engine cuts out for 0.5s intermittantly.

Here are my observations:
- Voltage between ground activation signal from DME (tested on the DME connector at pin 20) and + is dropping to nothing during the cut outs.
- Coil and/or injectors are also not recieving power during the cut outs.

Here is what I and various shops have tested/replaced:
- DME chip/unit
- KLR chip/unit
- throttle position switch
- mass airflow sensor (Autothority)
- speed sensor
- reference mark sensor
- fuel pressure
- fuel injectors

Here are some questions that I hope someone can answer:
- Under what conditions does the DME/KLR shut down the fuel pump and the rest of the ignition?
- How does the system detect fuel pressure?
- Any other advice?

Thanks,

Will

[Just4Fun]

Will

I'm currently having a similar experience (intermittent no start and stalling). Car is in shop now. Symptoms seam to point to reference and speed sensors. Moving sensors and swapping leads seamed to change the condition. I would be curious to find out how it goes with your car. DME and ECM new on my vehicle. My mechanic and I discussed replacing the ignition switch as suggested by Fr. Wilk

[PowerHaus944Turbo]

I would have mentioned that I replaced the DME relay, but didn't because it definitely is not the source of the problem since the DME is shutting it off. I suppose the ignition switch could potentially be responsible for shutting the DME off, but the engine cut outs seem to be just a little too regular to be due to a simple faulty connection (the car need not be in motion, and it happens EVERY time I run the car).

So... here are some of my predictions:
1. Knock sensor on engine is faulty.
2. Bad ground or short somewhere in the system.
3. Fuel delivery problem - fuel pump/filter... but I still don't know how the system detects the fuel pressure.
4. Voodoo curse.

Thanks,

Will

[Roger Hall]

Originally posted by PowerHaus944Turbo
I am currently using the Porsche DME/KLR test plan (WKD 453 920) for most of my information.

It sounds like you are on the right track. Whish I had answers for you, but my 924 doesn't have a DME. I had similar symptoms and they went away when I reuilt the fuel distributor. Since yours is EFI my guess would be two circuts control the injector one for the signal one to control the timing. I doubt its the fuel pump a .5 second interupt would probably not cause enough flow or pressure loss to cause the hicup.

FR WILK is the best person to answer this though. I am just guessing at this.

What is the DME/KLR test plan? Where did you get it? I am having some issues with my ECU. I am just guessing since I cant determin much from the current flow diagrams.