fuel pump wire mystery

[realem]

Porsche 1978 911 SC Targa. Recently had to rewire the fuse block. After rewire fuel pump would not go on when ignition was in the start position. At first I thought it was the relay or the fuel pump socket since I was able to fiddle with the relay in the socket and get the fuel pump to go on and the car would start. I also found that if I cranked the started the fuel pump must have gone on since the car started. However I have since been able to disconnect the brown wire from the relay socket or just cut off the brown wire pin and the fuel pump goes on and the car starts ok with about a 2 second cranking

Help


Mike

[Flat6pac]

Look at the back of the relay, there is embossed terminal numbers.
If you jump 30 and 87a, key on, that should run the pump.
Another terminal, the airflow sensor, can shut the pump down if it's not getting the signal that the motor is trying to start.
Bruce

[boyt911sc]

Originally Posted by realem

Porsche 1978 911 SC Targa. Recently had to rewire the fuse block. After rewire fuel pump would not go on when ignition was in the start position. At first I thought it was the relay or the fuel pump socket since I was able to fiddle with the relay in the socket and get the fuel pump to go on and the car would start. I also found that if I cranked the started the fuel pump must have gone on since the car started. However I have since been able to disconnect the brown wire from the relay socket or just cut off the brown wire pin and the fuel pump goes on and the car starts ok with about a 2 second cranking

Help


Mike

Mike,

When you get a chance search DKLever48's post about FP relay and socket operation. Everything you need to know is discussed and covered in that thread. There is also test procedures for all five (5) terminals.

Tony

[timmy2]

You have removed the safety shut off feature by removing the ground path for the coil.
Your pump will now run in the ignition run position all the time.
It isn't supposed to.
Only runs at start position and when engine actually runs.
The relay coil picks up disconnecting power to the fuel pump if the engine isn't running and key in the run position as a safety feature.

[realem]

Prior to rewire of the fuse block the fuel pump would always go on when the ignition was in the start position prior to cranking the starter. That was always my clue the fuel pump was working.

[Flat6pac]

Then there are wires crossed on the front of the fuel injection. The cold start injector and airflow sensor are reversed, or not plugged in. Common error
Bruce

[realem]

Are any of the fuse block wires associated with the coil, fuel pump as the only wires I moved were the wires in the fuse block itself and even then only wires in the 10 circuit fuse block were touched.

Thanks

[timmy2]

Originally Posted by realem

Prior to rewire of the fuse block the fuel pump would always go on when the ignition was in the start position prior to cranking the starter. That was always my clue the fuel pump was working.

Only supposed to be running while cranking or while running.
I'm guessing the safety switch on the air metering plate is unplugged or defective.