How to Test the Fuel Pump (Ford 4.0L)

If the fuel pump fails in your Ford 4.0L V-6 equipped SUV or pick up... it's not gonna' start and run.

Thankfully, Ford has made it super easy to test the fuel pump on your 4.0L Explorer (4.0L Ranger, 4.0L Aerostar or 4.0L Mountaineer) and in this article I'll show you how to do it.

Here are the contents of this article at a quick glance:

  1. Symptoms of a BAD Fuel Pump.
  2. FUEL PUMP TEST 1: Using Starting Fluid.
  3. FUEL PUMP TEST 2: Fuel Pressure Test with Gauge.
  4. Checking the fuel pump Inertia Switch.
  5. Which and Where to Buy a Fuel Pressure Gauge.
  6. Where to Buy the Fuel Pump and Save.
  7. Related Test Articles.

IMPORTANT: Gasoline is extremely flammable! Take all necessary safety precautions, be alert, be careful. Starting fluid and gasoline can ignite very easily.

En Español You can find this tutorial in Spanish here: Cómo Probar la Bomba de Combustible (Ford 4.0L) (at: autotecnico-online.com).

Symptoms of BAD Fuel Pump

A bad fuel pump will make your 4.0L Ford Explorer (Ranger, Aerostar, or Mountaineer) Crank but Not Start. Here are some more specific symptoms:

  1. The ignition coil pack is creating and delivering spark to all six spark plugs. So you know that the ignition system is not at fault.
  2. You've sprayed starting fluid (or carburetor spray) into the throttle body and your vehicle started, even if only momentarily.

Although the above list is a not a very complete list of symptoms... the theme that runs thru' them, and any other related symptom, is that the engine will crank and crank, but not start.

FUEL PUMP TEST 1: Using Starting Fluid

Using Starting Fluid to Check for a Lack of Fuel Condition. How to Test the Fuel Pump (Ford 4.0L)

Just in case you don't have a fuel pressure gauge handy, you can use starting fluid to see if the no start condition, of your 4.0L equipped Ford vehicle, is due to a lack of fuel.

This method is not the most accurate way of testing the fuel pump... but it doesn't mean it's not effective. The most important suggestion I can give you is to first make sure that all six cylinders are getting spark (thus eliminating the ignition system as the cause of the no start).

NOTE: If you haven't already checked the fuel pump inertia switch, do so before you start this test. For more info on the fuel pump inertia switch, take a look at this section: Checking the fuel pump Inertia Switch.

OK, to get this show on the road, this is what you'll need to do:

  1. 1

    Remove the intake air duct from the throttle body. You don't have to completely remove it, since you'll have to reconnect it in one of the next steps.

  2. 2

    Open the throttle, manually, and spray starting fluid down the bore. When you have sprayed a good squirt of starting fluid, quickly reconnect the Air Duct to the throttle body (you don't have to tighten the Hose Clamp).

    IMPORTANT: Reconnecting the intake air duct is a very important safety precaution in case you get a back-fire thru' the intake manifold.

  3. 3

    Once the intake air duct is back on the throttle body, have your assistant, inside the vehicle, crank the engine.

  4. 4

    You'll get one of two results with this test:

    1.) The engine will start momentarily and after a few seconds will die or.

    2.) The engine will only crank but not start at all.

OK, let's find out what your results mean:

CASE 1: If the engine started and ran for a few seconds: This means that the root cause of the no start your Ford vehicle is currently experiencing is due to a lack of fuel.

Usually, this also means that the fuel pump is BAD. But since we don't live in a perfect world... this could also mean a few other things like: the fuel pump fuse is blown, or the fuel pump relay is BAD.

Your next step is buy or rent a fuel pressure gauge and actually check fuel pressure (your local auto parts store, like AutoZone or O'Reilly Auto Parts will rent the fuel pressure gauge to you for free for a cash deposit which they'll return to you when you return the tool).

CASE 2: The engine did not start, not even momentarily: This usually means that a lack of fuel IS NOT the reason your car is not starting.

Now, remember what I said about this test not being very accurate? Well, I suggest you do one more test...

The next test is to actually verify the fuel pressure with a fuel pressure gauge. You can buy one or rent one (your local auto parts store, like AutoZone or O'Reilly Auto Parts will rent the fuel pressure gauge to you for free for a cash deposit which they'll return to you when you return the tool).