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).
Fuel Pump Pressure Specification
|1987-1993 2.5L TBI S10 Pickup||9-13 PSI||9-13 PSI|
|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:
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.
Disconnect the fuel line from the fuel filter.
NOTE: You need to disconnect the fuel line on the engine side of the fuel filter.
Connect the test adapter between the fuel line and the fuel filter.
Connect the fuel pressure gauge to the adapter.
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 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.