Possible DME Unit problem but not sure; DME relay is OK
 

Hi all, I have a '90 Carrera 2 Coupe. After verifying that both switches inside the DME relay are functional as well as trying another, brand new DME relay, the fuel pump won't run. However, bypassing the DME relay by jumping pins 3, 5, 7 does work. The fuel pump can be heard and the engine starts and runs.

It appears that pin 8 of the DME relay goes to pin 3 of the DME Unit's 55-pin connector. Does the DME Unit set this pin to ground to activate the fuel pump relay? I'm not sure if this is the source of the problem or something else. A voltmeter between pins 5 and 8 (for the fuel pump relay) of the DME Relay socket shows zero volts while cranking whereas there's 12 volts momentarily between pins 1 and 6 (for the other relay) while cranking.

Any help would be greatly appreciated!

Bryan

Contact Loren at www.systemsc.com. He's a sharp guy and will be able to advise you.

Good luck.

Here is the DME driver for the relay, it looks like a ground closure. This is from the FR Wilke site and for a 944 but I believe they are all the same. I think the other control circuit driving the base goes to the starter but not sure.

When you talk about pins on the DME relay, the factory wiring diagram referes to them as 87a, 87, 30 etc. Can you translate?

It also looks like a pretty rugged circuit, so the cracked solder joint may be a good guess. I would suggest some other troubleshooting steps first to be sure it is the DME.

http://forums.pelicanparts.com/uploa...1149529385.jpg

You guys are fantastic. I'm heading straight to the DME as advised. Nice to have angels on my side. Will keep you posted.

Bryan

Here's the DME pin # translation:

3, 5, 7 = 30, 87, 87b respectively.
8 = 85b
1, 6 = 86, 85 respectively.

I'll be investigating the control unit for loose connections this evening.

Bryan