Fuel Pump Doesn't Turn On?
 

I replaced the fuel pump on 1984 911 Carrera, but it does not turn on when I turn on the ignition. If I by pass the DME it will turn on, I have replaced the DME relay as well. Could the ignition switch be faulty?

Are all power lines and ground lines clean? Unfortunately, as these cars age their electrical reliability goes down unless you make it a periodic maintenance item to clean these things.

Have you got a multi-meter? Is there power getting to the pump? (You should be able to hear a high pitched whine coming from it).

The factory alarm system can also interrupt power to the fuel pump. If you have a factory alarm system you might want to check that as well.

My fuel pump won't actually run until you start the car or at least crank the engine over.

The pump will come on. I tested it by bypassing the DME. I've checked the grounds they seem to be ok. I found the battery to have a lost about 70% of it's charge, so I am recharging now. Hopefully it was the low charge that was causing the problem.

Charged the battery, and tried again but still isn't turning over.

My 84 Carrera does the same occasionly. In my case, it's the ignition switch. Try a jumper wire between the two terminals on the starter. If it turns over, your switch is most likely the problem.

Thanks sounds like a good idea. The ignition switch has always been finicky. Sometimes I have to turn the key several times to get it to crank. Does the fuel pump turn on if you turn the the key to the on position with out crankng? I thought it would, but another post said it wouldn't until the engine turned over.

fuel pump doesn't turn on till the flywheel is spinning. (unlike CIS)

The switch has to be cranking the engine before power gets to the DME relay. You will never get power to it by just turning on the key. The 84-89 Carrera's are not like other cars. The DME relay is also the fuel pump relay. There is no black or red relay in the fuse box up front. The relay is located under the drivers seat and mounted to one of the studs that anchors one side of the DME brain box.

Thanks. I put in a new DME relay, it'll crank but it won't turn over. Sometimes I have to turn the key a couple of times to get it to crank, and thought it might be the ignition switch that is the problem.