How To Test The Fuel Pump (1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995 4.3L V6 TBI Chevrolet S10 Pickup, GMC S15 Pickup, And GMC Sonoma)

The fuel pump on your Chevrolet S10 pickup, GMC S15 pickup or GMC Sonoma's 4.3L V6 TBI equipped engine can be tested with a fuel pressure test gauge.

In this tutorial, I'll walk you through how to do it step by step. You'll quickly determine if a fuel pump issue is causing an engine no-start or performance problem.

I'm also gonna explain how to use starting fluid to determine if the engine's no-start problem is due to a lack of fuel.

NOTE: TBI = Throttle Body Injection.

In Spanish You can find this tutorial in Spanish here: Cómo Probar La Bomba De Combustible (1988-1995 4.3L V6 Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

  • 4.3L V6 TBI Chevrolet S10 Pickup: 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995.
  • 4.3L V6 TBI GMC S15 Pickup: 1988, 1989, 1990.
  • 4.3L V6 TBI GMC Sonoma: 1991, 1992, 1993, 1994, 1995.

NOTE: You can find the fuel pump test for the 1992-1995 4.3L V6 Chevy S10 pickup (GMC Sonoma) equipped with CPI fuel injection here:

The fuel pressure test for the 1996-2003 4.3L S10 pickup (Sonoma) can be found here:

Symptoms Of A Bad Fuel Pump

A fuel pump failure generally causes 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 two reasons: Its quality and its brand name (it's not some cheap knock-off tool that'll only last one use). You can buy it here: Actron CP7838 Professional Fuel Pressure Tester (at amazon.com).

Fuel Pump Pressure Specification

Chevrolet
Year/Engine/Model KOEO KOER
1988-1995 4.3L TBI S10 Pickup 9-13 PSI 9-13 PSI
GMC
Year/Engine/Model KOEO KOER
1988-1995 4.3L TBI S15 Pickup and Sonoma 9-13 PSI 9-13 PSI

KOEO = Key On Engine Off.

KOER = Key On Engine Running.

TBI = Throttle Body Injection.

Using A Fuel Pump Pressure Tester To Test The Fuel Pump

To test the fuel pump's pressure, you'll connect a special fuel pressure tester adapter between the fuel filter and the fuel line that connects to the throttle body unit.

In photo 1 of 2, you can see how the fuel pressure tester's adapter connects to the fuel fuel filter.

Once the adapter is in place, you'll connect the fuel pressure test gauge to it.

The fuel pump pressure specification for the models covered by this tutorial is:

  • 9-13 PSI Key On With Engine Off.
  • 9-13 PSI Key On Engine Running.

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, let's get this show on the road:

  1. 1

    Place a shop towel under the fuel filter. The shop towel's job is to absorb any fuel that may leak when doing step 2.

  2. 2

    Disconnect the fuel line from the fuel filter.

    NOTE: You need to disconnect the fuel line on the engine side of the fuel filter.

  3. 3

    Connect the test adapter between the fuel line and the fuel filter.

  4. 4

    Connect the fuel pressure gauge to the adapter.

  5. 5

    When ready, ask your helper to cycle the key ON and OFF but don't crank the engine.

  6. 6

    Check your connections for fuel leaks. Resolve any fuel leaks before continuing to the next step.

  7. 7

    Crank the engine and check the fuel pressure gauge.

  8. 8

    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 confirms that a lack of fuel from the fuel pump is causing the engine to not start.

This test result usually confirms that the fuel pump has failed and needs to be replaced. When replacing the fuel pump, you'll also need to replace the fuel pump strainer and the 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.

Chevrolet Vehicles:

  • S10 Pickup 4.3L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995

GMC Vehicles:

  • S15 Pickup 4.3L
    • 1988, 1989, 1990
  • Sonoma 4.3L
    • 1991, 1992, 1993, 1994, 1995