How to test external fuel pump?

[Batz]

Hey all, i was wondering how to test if the external fuel pump works (the one outside the tank). Also i was wondering if it has some sort of valve/flap in it?

Thanks

[jlevie]

You can jumper the fuel pump relay (with ignition on) or apply power directly to the pump and listen or feel the pump to see if it is doing anything. But the crucial test is to tee a gauge into the rail supply line and see what the pressure is with the pump jumpered or the engine running. The pump can be running but be worn to the point that it is not pressurizing the rail. If the pump is running, but rail pressure is too low, pinch off the return line from the FPR. The pressure should instantly spike up to 80-90psi.

There is a check valve in the pump to prevent loss of rail pressure when the engine is off.

[Batz]

Alright, thanks a lot.

[efficient]

how much psi is supposed to be when the car is off?

[jlevie]

how much psi is supposed to be when the car is off?

It should hold normal rail pressure, or close to it. What pressure that will be depends on what E30 you have.