Porsche Repair: 93 968 porsche no power to the fuse for fuel pump, fuel pressure gauge, bosch relay

Question
i have no power to the fuse for the fuel pump.    the relay (dme) seems to be good.  

Answer
Hi Tim.

I only have an older wiring diagram for the 944, the predecessor to your 968, so what I'm looking at is dated...but often the wiring will be the same or similar in an area as straightforward as is the fuel pump.  

All I can see is one connection from the battery to the DME relay, and then all the other connections are directly with the Digital Motor Electronic Control Unit.  The DMEC will only trigger the Relay when all its sensor values are correct.  I'm not sure about the 944, but many engines will be "stopped" (meaning no power to the fuel pump) if the oil pressure is deemed 'too low'.

Unfortunately, I know of no way to test the DMEC, other than to replace it with a "known" "good" one.  This is black box voodoo at its best...or worst!  

Two things to look for or do first...I'd wire up a new universal Bosch relay ($7-8) directly from the ignition/battery to the fuel pump, using the same fuse or a new fuse.    This will allow you to start the engine temporarily to check for the correct functioning of the fuel pressure gauge.  If the gauge reads normal, you could use this temporary set-up to drive to your local friendly Porsche dealer.  They have all the $$$necessary$$$equipment$$$and$$$trained$$$technicians$$$ to help you.

I wouldn't run the temporary relay too long without knowing which sensor was causing the problem or if it were really the DME Relay afterall.

Let me know what you find...or if I can be helpful wiring up the temporary relay.

Dave