Although the electric fuel pump in your 2.5L Chevrolet S10 (GMC S15 pickup, GMC Sonoma) is located in the fuel tank, testing it is not difficult.
The best part is that you don't need expensive diagnostic equipment, as the fuel pump can be easily tested with an inexpensive fuel pressure tester. In this tutorial, I'll show you how.
I'll also explain how a starting fluid test can help you determine if the 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 (1987-1993 2.5L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.5L Chevrolet S10 Pickup: 1987, 1988, 1989, 1990, 1991, 1992, 1993.
- 2.5L GMC S15 Pickup: 1987, 1988, 1989, 1990.
- 2.5L GMC Sonoma: 1991, 1992, 1993.
Symptoms Of A Bad Fuel Pump
As you're already aware, the fuel pump's job is to provide the fuel the engine needs to start and keep running.
When the fuel pump fails, it will either not deliver any fuel or will not deliver enough fuel to the fuel injectors. This low or lack of fuel will generally cause one of two problems:
- An engine no-start problem.
- An engine performance problem (the engine starts and runs, but runs badly).
If the engine is getting just enough fuel to start but not enough to keep running, 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 |
| 1987-1993 2.5L TBI S10 Pickup | 9-13 PSI | 9-13 PSI |
| GMC | ||
|---|---|---|
| Year/Engine/Model | KOEO | KOER |
| 1987-1993 2.5L 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 check the fuel pressure, a special adapter is installed between the fuel line and the fuel filter (as shown in the illustrations above).
Once the adapter is in place, the fuel pressure test gauge is connected to it.
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.
CAUTION: Gasoline is a highly flammable liquid, take all necessary safety precautions and remain alert when working with gasoline.
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
Starting fluid can be used to determine if a lack of fuel is causing an engine no-start problem.
I've used starting fluid to diagnose the cause of many engine no-start problems over the years and I can tell you this test works.
While the starting fluid test is not the most accurate way to diagnose a bad fuel pump, it will steer your troubleshooting efforts in the right direction.
OK, let's begin:
- 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 2.5L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials
You can find a complete list of 2.5L Chevy S10 pickup, GMC S15 pickup, And GMC Sonoma tutorials here:
Here's a sample of the tutorials you'll find in the index:
- How To Test Engine Compression (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test For A Blown Head Gasket (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test The TPS (1987-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test The MAP Sensor (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
If this info saved the day, buy me a beer!
