OK, so the long story short goes something like this. My buddy bought a VERY used 1983 Porsche 944. Overall, the car is solid. The maniac who sold the car had the fuel pump/DME wire spookily rigged under the hood, but some duct tape and a bit of twisting later the beast was running. It does run well. Mileage is low. Had a million typical old used 944 wiring problems. That aside, up on the dolly it went and into the garage.

So now a few days later, all the lights are working, the power windows are back in shape, the interior smells much less like bums lived in it, and there are a new set of Recaros ready to install. The suspension is good, the brakes are in good shape, and the window seals are nice and tight. It is well on it’s way to being reborn again hard. The racing team would like to see it roll in the 2007 season. So why are we here looking for knowledge? The bastard has developed the dreaded DME “no spark” problem…we think. So in our troubleshooting extravaganza we have thoroughly perused the factory service manual and run almost every diagnostic that does not require and oscilloscope.

-Yes, there is power to the DME computer. (have two and both appear to be good)
-The DME relay is working.
-The grounds are all clean and showing good ground.
-The crank and idle position sensor are both new and in good shape with signal.
-There is negative pulse at the coil when cranking.(no positive pulse)
-The coil is working.
-Tried the three prong relay jumper to no avail.
-Fuel pump is working as well for reference.
-No blown fuses or other strange goings on.

So our last attempt this evening found us with this conundrum. When we turn the key on we get positive signal at the positive terminal on the coil. When the key is turned, the signal goes bye-bye. The ignition relay near the heater box appears to be working, and we have backup relays that we’ve tested.

SO WHAT GIVES??

 

Have you checked to see if the rotor spun? I ran into a similar situation and the bolt that held the rotor fell out and the rotor spun into a no start condition. Just a thought.

 

Two things to check: The DME itself. You can open it and check for loose solder joints, or bang on it a few times and see if the car starts. If that all checks out, then I would look at the engine wiring harness where the speed and reference sensors connect. I am seeing these go bad on a weekly basis. Wiggle the harness end of the connections and see if it starts.

I take it you are not getting any tach bounce when you crank the engine over (it should move ever so slightly)

 

The wiringharness looks good and clean ,rotor spins and the DME is good. Key in on
pos everyhting is as it should, when turning the engine over all power is lost. No lights,
no gauges, no spark and no fuel pump. Thanks Jay

 

So it isn't turning over at all? Try a new battery.

 

I'd also check, very carefully, all my electrical grounds. Could it be a bad ignition switch?

 

After rereading the thread, I'd say if the power is going away once you start cranking it, (lights, etc, as you posted) you have either a bad ignition switch, a bad battery cable, or something is broken, like the inside of the terminal post, inside the battery. The last one is pretty common on side-post batteries, less so on top-post, but it can happen even on new batteries if a forklift operator gets careless and drops a pallet, or puts it down too roughly, especially in cold weather.