Power to the DME Relay

[Emnyama944]

I need some help troubleshooting a no start issue on my 944 turbo, the short question is, should there be 12 volts to the DME when the key is in the on position or do we only get 12 volts when we turn the key to start the car?

The car runs with the DME relay jumped but I've tried three different DME relays and though the car turns over a few times it dies very quickly. I have a VEMS ECU and the car does exactly the same thing, but I found there is only 12 volts to the ECU when I jump the DME relay so I'm wondering if I'm not getting power to the relay.

Any help would be appreciated.

Rudi

[944 Ecology]

As you can see from this diagram, turning the ignition switch on provides power to the DME... once the DME senses the engine rotation (via the flywheel sensors), it provides a ground for the fuel pump half of the DME relay, turning on the fuel pump.

[Emnyama944]

Thanks George, I've been troubleshooting this issue for a while and I was starting to doubt myself about getting 12 volts at pin 86 on the DME relay, the most I get is about 0.5 volts. The question now is, why am I not getting power to pin 86? I've jumped the alarm to make sure it's not causing any issues.

[kdjones2000]

What year is your car?

The alarm and airbag circuitry come into play on 87+ cars...

[944 Ecology]

Originally Posted by Emnyama944

Thanks George, I've been troubleshooting this issue for a while and I was starting to doubt myself about getting 12 volts at pin 86 on the DME relay, the most I get is about 0.5 volts. The question now is, why am I not getting power to pin 86? I've jumped the alarm to make sure it's not causing any issues.

It's probably a bad connection or wire to pin 86 from the ignition switch. Check your circuit.

[Emnyama944]

Originally Posted by kdjones2000

What year is your car?

The alarm and airbag circuitry come into play on 87+ cars...

Thanks, I've bypassed the alarm and the car has been butchered a little bit over the years so it's possible the wiring is messed up, it's an 87' but doesn't have an airbag.

I spent most of the day going through the wiring diagrams and trying climbing under the dash to trace the possible routs of the wires, I was hoping there might be a common issue but I guess it's time to curl up under the dash.

[kdjones2000]

This might help you. It's for an '88, but '87 should be similar. The airbag needs to be taken out properly in order for the DME to get voltage.

http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/1011953-dme-relay-quiz.html