My son has a 2003 sonoma 4.3L his fuel pump has been intermittently operating. We swapped fuel pump relays, and changed the pump. The problem came back, power not getting to the pump. I checked for power at the fuel pump relay and am not getting any power there with the key turned on. I've heard the oil pressure switch also sends power out to the fuel pump. But there is only 1 wire on the switch. I've heard it could be the ECM, but I believe in his truck it is called a PCM. We picked up a chiltons but the schematic isn't exact. I believe the fuel pump relay gets power from the ignition switch when turned on. :banghead: Help.

If you hot wire the pump will it run?

Did you check the fuel pressure and where did you get the fuel pump?GMs will not run with low fuel pressure.

The PCM activates the fuel pump relay through a dark green with white tracer wire, (bottom side of the underhood fuse panel). It is HOT when the key is in the START position. It is also HOT when the key is in the RUN position provided the engine is running. If the key is in the RUN position and the engnie is not running, the PCM will deactivate the relay after 2 to 3 seconds. In the underhood fuse panel there is a recessed, empty terminal near the fuel pump relay. This is the fuel pump prime connector and goes directly to the fuel pump. If you apply battery voltage to the terminal, the fuel pump should run continously. While it is running, you can wiggle connectors and look for poor connections, broken wires, etc etc.

The relay circuits are as follows:
#85 Hot with key in start or run position*(see above)
#86 Ground
#30 Hot at all times (ECM "B" fuse)
#87 To fuel pump and prime connector