TEST 2: Fuel Pressure Test (Engine Starts)

How To Test The Fuel Pump (1993, 1994, 1995 3.2L Isuzu Rodeo And Honda Passport)

If the engine starts and runs, but doesn't run optimally, then there's a good chance the fuel pump is not sending enough fuel to the fuel injectors.

We can easily verify if the fuel pressure is within specification by connecting a fuel pressure gauge to the Schrader valve (see photo above).

The fuel pressure specification, with the engine running, is OK is: 25-30 PSI (with fuel pressure regulator connected to its vacuum hose).

Any fuel pressure less than 25 PSI, with the engine running, let's you know that the fuel pump is failing.

NOTE: If you don't have a fuel pressure gauge, take a look at the section: Where To Buy A Fuel Pressure Test Gauge.

OK, let's get started with this test:

  1. 1

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

  2. 2

    Connect the fuel pressure gauge to the Schrader valve.

  3. 3

    Crank and start the engine.

  4. 4

    Your fuel pressure gauge should register: 25 to 30 PSI.

Let's take a look at what your results mean:

CASE 1: The fuel pressure gauge registered 25 to 30 PSI. This is the correct and expected test result.

If the engine is experiencing a driveability problem, then with this test result you can conclude that the fuel pump is not behind it.

CASE 2: The fuel pressure gauge registered a pressure less than 25 PSI. This test result tells you that the fuel pump is failing.

TEST 3: Checking The Fuel Pump Fuse

If in TEST 1 the fuel pressure gauge reported a fuel pressure of 0 PSI, then we need to make sure that the fuel pump fuse is not blown.

On the 1993, 1994, and early 1995 3.2L Isuzu Rodeo, this is fuse #9 of the underhood fuse/relay box (see illustration 1 of 2).

On the mid 1995 and later 3.2L Isuzu Rodeo, the fuel pump fuse is fuse EB-11 of the underhood fuse/relay box (see illustration 2 of 2).

These are the test steps:

  1. 1

    Remove the plastic dust cover from the underhood fuse box.

  2. 2

    Locate the fuel pump fuse.

    1993, 1994, and early 1995 3.2L Isuzu Rodeo: This is fuse #9 of the underhood fuse/relay box.

    Mid 1995 and later 3.2L Isuzu Rodeo: This is fuse EB-11 of the underhood fuse/relay box.

  3. 3

    Remove the fuse and make sure that it's not blown.

Let's take a look at what your results mean:

CASE 1: The fuel pump fuse IS NOT blown. This is the correct and expected test result.

If in TEST 1 you got a fuel pressure reading of 0 PSI, then you can conclude that the fuel pump is bad and needs to be replaced.

CASE 2: The fuel pump fuse is blown. Replace the fuse and retest.

If the fuse gets blown again, then this usually means one of two things: The fuel pump has suffered an internal short-circuit problem or the wiring between the fuse and the fuel pump has suffered an open-circuit problem.

Isuzu Vehicles:

  • Rodeo 3.2L
    • 1993, 1994, 1995

Honda Vehicles:

  • Passport 3.2L
    • 1994, 1995