You can easily find out if the fuel pump is good or bad with a fuel pressure test performed with a fuel pressure gauge.
In this tutorial, I'll explain how to do the fuel pressure test with a fuel pressure tester. With your test results, you can quickly determine if the fuel pump has failed or is failing.
I'll also explain how to use starting fluid to determine if an engine no-start problem is due to lack of fuel.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Bomba De Combustible (1996-2003 4.3L V6 Chevrolet S10 Pickup, GMC Sonoma) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 4.3L V6 Chevrolet S10 Pickup: 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003.
- 4.3L V6 GMC Sonoma: 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003.
- 4.3L V6 Isuzu Hombre: 1998, 1999, 2000.
NOTE: You can find the fuel pump test for the 1988-1995 4.3L V6 Chevy S10 pickup (GMC S15 pickup, GMC Sonoma) equipped with TBI and CPI fuel injection here:
- How To Test The Fuel Pump (1988-1995 4.3L TBI Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The Fuel Pump (1992-1995 4.3L CPI Chevrolet S10 Pickup, GMC Sonoma).
Symptoms Of A Bad Fuel Pump
Although it doesn't happen overnight, the fuel pump will fail. When it does, it'll generally cause one of two problems:
- An engine no-start problem.
- An engine performance problem (the engine starts and runs, but runs badly).
When the fuel pump supplies barely enough fuel to start the engine, you'll see one or more of the following symptoms:
- Engine takes longer than usual to start (extended cranking).
- Engine idle is very rough.
- Engine backfires thru' the intake manifold under load.
- Engine starts, then dies.
- Lack of power when accelerating the vehicle under load.
A fuel pump pressure test will help you determine if a fuel pump failure is causing an engine no-start or an engine performance problem.
Where To Buy A Fuel Pressure Test Gauge
The Actron CP7838 Professional Fuel Pressure Tester is my go-to tester for three reasons:
- Its a quality tool (not some cheap knock-off tool that'll only last one use).
- It fits the GM Schrader valve.
- It doesn't cost an arm and a leg.
You can buy it here: Actron CP7838 Professional Fuel Pressure Tester (at amazon.com).
Fuel Pump Pressure Specification
|1996-2000 4.3L S10 Pickup||60-66 PSI||50-63 PSI|
|1996-2000 4.3L Sonoma Pickup||60-66 PSI||50-63 PSI|
KOEO = Key On Engine Off.
KOER = Key On Engine Running.
Using A Fuel Pump Pressure Tester To Test The Fuel Pump
To test the fuel pressure, we'll hook up a fuel pressure gauge to the Schrader valve located on the fuel line entering the fuel injector assembly (on the back and top of the intake manifold -see photo 2 of 2 above).
Once the fuel pressure gauge is connected to the Schrader valve, we'll start the engine and see what fuel pressure the gauge records.
If the fuel pressure tester shows the specified fuel pressure, you can conclude that the fuel pump is working properly.
When the fuel pump is bad, you usually see one of two things:
- A fuel pressure of 0 PSI.
- A fuel pressure below the specified value.
NOTE: If you don't have a fuel pressure tester with the correct adapter, see my recommendations here: Where To Buy A Fuel Pressure Test Gauge.
OK, these are the test steps:
Remove the plastic dust cap from the Schrader valve.
Place a shop towel around the Schrader valve and fuel line. The shop towel's job is to absorb any fuel that may leak when doing step 3.
Connect the fuel pressure gauge to the Schrader valve.
When ready, ask your helper to cycle the key ON and OFF but don't crank the engine.
Check your connections for fuel leaks. Resolve any fuel leaks before continuing to the next step.
Crank the engine and check the fuel pressure gauge.
Your fuel pressure gauge should register the specified fuel pressure.
Let's interpret your test results:
CASE 1: The fuel pressure test gauge registered 0 PSI. This test result indicates that the fuel pump is not supplying fuel to the fuel injector assembly.
The result of this test usually confirms that the fuel pump has failed and should be replaced. When replacing the fuel pump, you will also need to replace the fuel pump strainer and fuel filter.
CASE 2: The fuel pressure gauge registered the indicated fuel pressure specification. This test result tells you that the fuel pump is functioning correctly and sending fuel to the fuel injectors.
If the engine isn't starting, You can conclude that the fuel pump IS NOT behind the issue.
CASE 3: The fuel pressure gauge registered a fuel pressure way below the specification. This test result tells you that the fuel pump is failing. Replace the fuel pump, the fuel pump strainer, and the fuel filter.