hjalmarsson41

Will try first thing in the morning!

hjalmarsson41

When I unplug the DME connector at the DME and measure the green and black wires mounted on the coil I get these readings:

Ignition off:
+ (at the battery) to green wire(mounted on coil): 12.95 V
+ (at the battery) to black wire(mounted on coil): 12.95 V

Ignition on:
- (at the battery) to green wire(mounted on coil): 12.8 V
- (at the battery) to black wire(mounted on coil): 12.8 V

I did the same test with the wires loose, i.e not mounted on the coil:

Ignition off:
either + or - (at the battery) to green wire(NOT mounted on coil): 0 V
+ (at the battery) to black wire(NOT mounted on coil): 12.9 V

Ignition on:
either + or - (at the battery) green wire(NOT mounted on coil): 0 V
- (at the battery) to black wire(NOT mounted on coil): 12.85 V

hmm... guessing a fault with the DME computer?

orig944

That is not a good sign for the DME. Perhaps you can find another late 944.5+ or 924S owner in your area and try your DME in their car to confirm. Most likely the ignition driver transistor has failed, and now leaks enough current to ground that the coil does not reach enough voltage to spark. The schematic of a similar DME that is on Clark's Garage shows a couple of other components on that wire that it could be as well.

If you know someone electrically inclined, it may be possible to repair your DME. The transistor is a specialty high voltage device that is no longer manufactured, but I found some available on ebay. (Phillips or NXP ON1012.) Whomever does this should diagnose to the actual failed component before buying one though.

Meanwhile, while you get this sorted out, you should unscrew your spark plugs and let any accumulated fuel evaporate out.

hjalmarsson41

I see... I will remove the DME and check it myself and see if I can find anything, but that will be a project for the winter. I have some experience tinkering with soldering and chips from my years in military aviation so I can try atleast.

Thank you very very much for all the help! this has been driving me up a wall and your help has really made things clear. For your info, my local porsche dealer was nowhere near as good a help as all your info