How To Test The Fuel Pump -Dual Fuel Tanks (1993-1996 Ford F150, F250, F350)

Testing the front or rear tank fuel pump on your 1993-1996 Ford F-Series pickup, to find out if one (or both) are bad, is not difficult.

In this tutorial, I'll explain how to test them with a fuel pressure test gauge. With your test results you'll be able to find out if a fuel pump is bad or not.

APPLIES TO: This tutorial applies to the following vehicles:

• Ford F150 (4.9L, 5.0L, 5.8L): 1993, 1994, 1995, 1996.
• Ford F250 (4.9L, 5.0L, 5.8L): 1993, 1994, 1995, 1996.
• Ford F350 (4.9L, 5.8L, 7.5L): 1993, 1994, 1995, 1996.

RELATED WIRING DIAGRAMS:

• Fuel Pump Wiring Diagram -Dual Fuel Tanks (1993-1995 Ford F150, F250, F350).
• Fuel Pump Wiring Diagram -Dual Fuel Tanks (1996 Ford F150, F250, F350).

Symptoms Of A Bad Fuel Pump

The fuel pump's job is to deliver the fuel the engine needs as soon as you crank and start the engine.

Unfortunately, the fuel pump will fail sooner or later. When it does, it'll usually fail in one of two ways:

1. The fuel pump will fail completely and not send any fuel to the engine. This will cause the engine to not start.
2. The fuel pump does not send enough fuel to the engine. The engine will start but it'll run with engine performance problems.

When the fuel pump begins to fail, but supplies only enough fuel to start the engine, you'll usually see one or more of the following symptoms:

• Engine backfires thru' the intake manifold when the engine is under load.
• The check engine light illuminates with lean air/fuel mixture codes.
• The check engine light illuminates with a MAP sensor trouble code.
• Lack of power when accelerating the engine under load.
• Engine stalls when the engine is accelerated under load.

Thankfully, testing the fuel pump is not hard and in this tutorial I'll explain how to do it.

Where To Buy A Fuel Pressure Test Gauge

You'll need a fuel pressure test gauge to find out if either fuel pump (in the front or rear tank) is bad or not.

The fuel pressure test gauge kit that'll connect to your Ford pickup's Schrader valve and that I recommend for its low price and durability is the: Actron CP7838 Professional Fuel Pressure Tester.

The following fuel pressure test gauges all have the Ford Schrader valve adapter you need to test the fuel pump:

TEST 1: Checking The Fuel Pump Inertia Switch

The fuel pump inertia switch's job is to cut power to the fuel pumps in case of a collision (vehicle impact).

In some cases, even jumping the curb will cause it to initialize and cut power to the fuel pumps.

If it isn't reset, the engine will crank but not start due to a lack of fuel (with either fuel tanks selected).

So before testing the fuel pumps' fuel pressure, we'll check to see if just resetting it will get the engine started.

LOCATION: The fuel pump inertia switch is located behind the passenger side plastic kick-panel.

NOTE: This test only applies if the engine DOES NOT start when either tank (FRONT or REAR) is selected (on the fuel tank selector switch).

If the engine starts with one tank selected (but not the other), then the fuel pump inertia switch does not need to be reset and your starting point is TEST 2.

OK, these are the test steps:

1. 1

   Remove the passenger side plastic kick-panel to access the fuel pump inertia switch.

2. 2

   Push down on the red button on top of the switch.
   
   This button is on top of the fuel pump inertia switch.

3. 3

   You should hear a "click" when you push down on the button.
   
   Whether you hear a click or not, continue on to the next step.

4. 4

   Crank and start the engine.

5. 5

   You'll get one of two results:
   
   1.) The engine started.
   
   2.) The engine did not start.

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

CASE 1: The engine started with either tank selected. This tells you that the fuel pump inertia switch was activated and was cutting power to the fuel pumps.

Now that the fuel pump inertia switch has been reset, it's allowing power to reach the fuel pumps.

CASE 2: The engine DID NOT start when the FRONT tank was selected (but started with the REAR tank selected). Your next step is to check the FRONT tank fuel pump fuel pressure. Go to: TEST 2: Fuel Pump Pressure Test.

CASE 3: The engine DID NOT start when the REAR tank was selected (but started with the FRONT tank selected). Your next step is to check the REAR tank fuel pump fuel pressure. Go to: TEST 2: Fuel Pump Pressure Test.

CASE 4: The engine DID NOT start with either tank selected. This test result usually indicates a problem with:

• The fuel pump relay.
• The fuel tank selector switch.
• The fuel pump inertia switch.

Although it's beyond the scope of this tutorial to test these 3 components, your next step is to test each one.