Help with Turbo fuel pumps ( John Walker??)

[9dreizig]

Ok I've done a search and read the suggestions and am still at a loss. I can't get my fuel pumps to engage unless I jumper the front relay. I've tried the jumper of the overboost connector, with no success. The engine is running great with the relay jumped.
Any suggestions ? Also this is a engine that has not been in the car before so there are some unknowns on the wiring harness.
It's a 1980 930 with a 79 engine
Todd

[dean]

Let me see if I can remember the Compicated Icky System.

There are two things that power the fuel pump relay coil. One is when the starter cranks. And the other is when the air flow sw. senses flow. (I can't remember if it closes or opens)

Do you have a wiring manual for the turbo? That would really help.

[rotorhead]

Thereis another important relay in the fuel pump system, the overboost relay (Yellow one in the engine compartment) it cuts power to the front relays in the event of an overboost of 1.2bar or greater. You may want to check its function and the function of the overboost switch. (Funny.... second post I have made tonight about this relay)

If you need a wiring diagram for the 930 let me know.

[john walker's workshop]

the white wire on the intake mounted overboost sender needs to be attached to the sender, which grounds it during normal operation. also check the sender to be sure it's not "open". the sender breaks it's ground on overboost and with the help of the overboost relay, kills the front fuel pump relay function. also, the overboost relays develop cracks in the solder around the pins, so pop the case off and inspect the joints with a magnifying glass and resolder if needed.

[9dreizig]

Thanks everyone, I think I found it. When I ground the white wire it fires up and runs like a clock!