This tutorial will show you how to test the fuel pump relay on your 1997, 1998, 1999 Chevrolet/GMC full-size Pick Up, Suburban, Tahoe, or Yukon.
It'll also show you how to bench test the fuel pump relay in a step-by-step way to find out if it's defective or not.
Contents of this tutorial:
- Before You Start Your Fuel Pump Relay Diagnostic.
- TEST 1: Swapping Out The Fuel Pump Relay.
- TEST 2: Making Sure The Fuel Pump Relay Has Power.
- TEST 3: Bypassing The Fuel Pump Relay.
- TEST 4: Bench Testing The Fuel Pump Relay.
- Fuel Pump Circuit Diagram.
- Where To Buy The Fuel Pump Relay.
- More GM 4.3L, 5.0L, and 5.7L Tutorials.
Before You Start Your Fuel Pump Relay Diagnostic
It's very important that you start off your fuel pump relay diagnostic by first testing the fuel pump pressure with a fuel pressure test gauge.
If the fuel pump relay IS NOT activating the fuel pump, the fuel pressure test gauge will register 0 PSI when cranking the engine.
If the fuel pump relay is activating the fuel pump, then it'll register about 56-62 PSI even if the engine does not start. Any fuel pressure below 50 PSI and the engine will NOT start.
If you do see any fuel pressure below 50 PSI, the fuel pump although working, is not creating enough pressure to start the engine and is defective.
Testing the fuel pump's pressure with a fuel pressure gauge will help you avoid replacing good parts and/or getting the wrong diagnostic test result.
If you don't have a fuel pressure test gauge, you can borrow one from your local auto parts store (like AutoZone, O'Reilly Auto Parts, etc) for a small deposit that you'll get back when you return it.
The following tutorial may be of help: Troubleshooting The Fuel Pump (GM 4.3L, 5.0L, 5.7L) (at: troubleshootmyvehicle.com).
TEST 1: Swapping Out The Fuel Pump Relay
The easiest and fastest way to find out if the fuel pump relay is bad is to swap it out with another.
The awesome thing is that you don't have to run out and buy another, since you can swap it out with the AC relay.
The AC relay is located in the same under-hood fuse/relay box the fuel pump relay is in (see illustration above).
These are the test steps:
Locate the fuel pump and AC compressor relays in the under-hood fuse and relay box.
Swap the relays.
We're using the AC relay because it won't affect any other system when trying to crank up the engine.
Have a helper crank the engine.
The fuel pressure test gauge should show 56-62 PSI and the engine should start if the previous relay was defective.
Let's take a look at what your test results mean:
CASE 1: The fuel pressure test gauge recorded 56-62 PSI after swapping the relay. This test result confirms that the fuel pump relay is defective and needs to be replaced.
CASE 2: The fuel pressure test gauge recorded 0 PSI. This could mean that the fuel pump relay is not the problem behind the no-start condition but to be sure, I suggest going on to the next test step: Making Sure The Fuel Pump Relay Has Power.