No power to Fuel Pump?

JOSH GOFF

MEMBER
1988 CHEVROLET SILVERADO
5.7L
V8
4WD
AUTOMATIC
93,000 MILES

I originally had a problem with the truck not starting. I replaced the fuel relay switch and also put in a brand-new fuel pump. I took out out some of the fusible links that go from the power rail to the relay switch, and fuel pump. Started up and ran fine. I drove it around for a few weeks. Then it sat for a few weeks. Went to start it and nothing. No power at the fuel pump, however, there is power at the power rail and relay. I do have spark. The truck will start with starting fluid, but then die because of no fuel.

Sunday, October 1st, 2023 AT 10:41 AM

2 Replies

AL514

MECHANIC
5,499 POSTS

Hello, is there a reason you took out the Fusible links? And at the Fuel pump relay location if you take the relay out, you should have power to 2 of the pins when you crank the truck over. This system has the ECM sending 12volts to the relay control side which activates it. For the other relay pins, one goes to ground which is on the control side, so the ECM sends out 12volts and the other pin for that side is always grounded. You can check the ground by hooking at 12v test light to Batter positive and touching that pin with the relay out and it should light up bright, Ill post a diagram of the fuel pump relay circuit.
On these older trucks, the relay pins on the underside of the fuse/relay box tend to corrode and break off, and you will lose ground or power, but verify first that there is power (12v) coming from the ECM to the relay location with it out.
Does this truck only have 1 gas tank?
Here is some service info on the fuel pump relay operation. It looks like there is a 20Amp Fuel Pump fuse after the relay. Did you run direct wires when you took out the Fusible Links?

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

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Monday, October 2nd, 2023 AT 11:02 AM

KEN L

MASTER CERTIFIED MECHANIC
54,144 POSTS

So, this truck has an oil pressure cut out switch to help save the engine if there is no oil pressure I would make sure the engine oil is clean and full and if so try to jump the connector at the switch to see if it starts, if so replace the sensor and also check the oil pressure of the engine. Here is the location of the switch and the fuel pump system wiring diagrams so you can see how it works. Please go over this guide as well:

https://www.2carpros.com/articles/how-to-manually-check-engine-oil-pressure-step-by-step-guide

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