Fuel pump not working?

FREDO87

MEMBER
1987 GMC S15
2.8L
6 CYL
2WD
AUTOMATIC
161,263 MILES

Fuel pump not turning on when you turn the key on relays new. I check the wiring, fuel pumps brand new I just replaced it today. When you jump it from the relay it turns on but when you use the key it don't turn on.

Thursday, December 22nd, 2022 AT 5:19 PM

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,133 POSTS

Hi,

If you are able to jump the relay and the pump runs, then the problem is on the primary side of the relay.

Power is supplied to the primary side via the ECM. The primary side is then sent to ground to complete the circuit. When that happens, the secondary side (the side you jumped) closes and power is sent to the pump.

So, here is what I need you to do: Remove the relay. One of the pins will have power at all times (secondary side). Another one will have power only when the key is on or in the start position. I need you to check for power. If it is present, then confirm there is a ground path for the primary side.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Check this and let me know what you find. Also, I attached the wiring schematic below for your review. The items in red are what was jumped to turn the pump on. The highlighted area is the primary side and that is the area of interest.

Take care and Merry Christmas.

Joe

See pic below.

Image (Click to make bigger)