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.
Contents of this tutorial:
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.
1992-1995 CPI FUEL PUMP TESTS: 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:
1996-2003 FUEL PUMP TESTS: The fuel pressure test for the 1996-2003 4.3L S10 pickup (Sonoma) can be found here:
ENGINE NO-START DIAGNOSTICS:
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).
Disclosure: As an Amazon Associate, I earn from qualifying purchases. Buying through these links helps support this site at no extra cost to you. Thanks for your support —it really means a lot!
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
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
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
Connect the test adapter between the fuel line and the fuel filter.
- 4
Connect the fuel pressure gauge to the adapter.
- 5
When ready, ask your helper to cycle the key ON and OFF but don't crank the engine.
- 6
Check your connections for fuel leaks. Resolve any fuel leaks before continuing to the next step.
- 7
Crank the engine and check the fuel pressure gauge.
- 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.
The Starting Fluid Test
The starting fluid test has been my go-to test for diagnosing an engine no-start problem from day one of my automotive repair career.
And when I started, most vehicles had carburetors and throttle body fuel injection systems (TBI) were just coming online.
The cool thing about using starting fluid (to diagnose an engine no-start issue) is that it let's you know right away if a lack of fuel is keeping the engine from starting.
The most important thing to remember when performing a starting fluid test is that you first need to make sure that all six spark plug wires are sparking (with a spark tester).
IMPORTANT: If you haven't checked all six spark plug wires for spark yet, please do so before performing the starting fluid test. I recommend using a dedicated spark tester for the spark test.
OK, these are the test steps:
- 1
Remove the cover from the air cleaner assembly.
You don't have remove the air cleaner assembly from the engine (best to leave it in place). - 2
Open the throttle manually, and spray starting fluid down the bore.
- 3
When you have sprayed a good squirt of starting fluid, quickly install the air cleaner assembly's cover (you don't have to tighten the nut).
Reinstalling the air cleaner assembly's top is a very important safety precaution in case you get a back-fire thru' the intake manifold. - 4
Crank the engine once you've place the cover back on the air cleaner assembly.
- 5
You'll get one of two results with this test:
1.) The engine will start momentarily and after a few seconds will die.
2.) The engine will only crank but not start at all.
OK, let's interpret your test results:
CASE 1: The engine started and ran for a few seconds. This test result confirms that the engine isn't starting due to a lack of fuel.
The most likely cause of this lack of fuel is a bad fuel pump.
CASE 2: The engine did not start, not even momentarily. This test result tells you that the engine's no-start problem IS NOT due to a lack of fuel.
It's important to note that this the accuracy of this test result depends on having all six spark plug wires sparking.
More 4.3L Chevrolet S10, GMC S15 And GMC Sonoma Diagnostic Tutorials
You can find a complete list of diagnostics tutorials for the 4.3L V6 S10, S15, and Sonoma in this index:
Here's a small sample of the tutorials you'll find:
- How To Test Engine Compression (1988-2003 4.3L V6 Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test For A Blown Head Gasket (1988-2003 4.3L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The EGR Valve (1996-2001 4.3L V6 Chevrolet S10 Pickup, GMC Sonoma).
- How To Retrieve OBD I Trouble Codes (1988-1995 4.3L V6 Chevrolet S10 Pickup, GMC Sonoma).
If this info saved the day, buy me a beer!
