How To Test The Fuel Pump (Ford 4.0L Explorer, Aerostar And Mercury Mountaineer)

If the fuel pump fails, your Ford 4.0L V6 equipped SUV or mini-van is not gonna' start and run.

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

NOTE: You can find the 4.0L Ford Ranger (Mazda B4000) fuel pump test tutorial here:

• How To Test The Fuel Pump (1991-2011 Ford 4.0L Ranger And Mazda B4000) (at: easyautodiagnostics.com).

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

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

APPLIES TO: This tutorial applies to the following vehicles:

• 4.0L V6 Ford Aerostar: 1991, 1992, 1993, 1994, 1995, 1996, 1997.
• 4.0L V6 Ford Explorer: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
• 4.0L V6 Mercury Mountaineer: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.

Symptoms Of A Bad Fuel Pump

A bad fuel pump will make your 4.0L Ford Explorer (Aerostar, or Mercury Mountaineer) crank but not start. Here are some more specific symptoms:

• 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.
• 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.

Where To Buy A Fuel Pressure Gauge

Owning a fuel pressure gauge is now becoming a must. All vehicles now use an electrical fuel pump to deliver fuel (under high pressure) to the fuel injectors and the best way to diagnose this fuel pump is with a fuel pressure gauge.

Thankfully, in all of the Ford 4.0L V6 equipped vehicles, Ford was kind enough to put a Schrader valve on the fuel injector rail where you can tap into the fuel system and check its performance.

A fuel pressure gauge can cost you as little as $40 (US) or as much as $200 (US). The price difference depends on what type of fuel pressure gauge set you buy, this means either buying a non-professional technician grade tool or a professional technician grade too. Whichever one you buy, it's an investment that will pay for itself many times over.

Your local parts house will have a fuel pressure gauge set to sell you, although you'll pay more for it and it won't be a professional grade tool (if that's what you're looking for).

TEST 1: Fuel Pressure Test With Gauge

As mentioned at the beginning of this tutorial, testing the fuel pump with a fuel pressure gauge is very easy.

What makes it easy is that you'll find a Schrader valve on the fuel injector rail that you can connect a fuel pressure gauge to (see: Location Of The Fuel Pressure Schrader Valve Test Port).

Using a fuel pressure gauge is one of the most accurate ways to ensure that enough fuel reaches the fuel injectors.

If you don't own one, you can run down to your local AutoZone or O'Reilly Auto Parts store and borrow one from them (for a small cash deposit, which you'll get back when you return the tool).

If you're interested in buying one, take a look at my recommendations here: Where To Buy A Fuel Pressure Gauge.

You can find the fuel pressure specifications here:

• Fuel Pressure Specifications (1991-1997 4.0L Ford Aerostar).
• Fuel Pressure Specifications (1991-2010 4.0L Ford Explorer, Mercury Mountaineer).

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, let's get started with this test:

1. 1

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

2. 2

   Install the Ford Schrader valve adapter on the Schrader valve.

3. 3

   Connect the fuel pressure gauge to the Schrader valve adapter.

4. 4

   When ready, ask your helper to cycle the key ON and OFF but don't crank the engine while checking for fuel leaks.
   
   If no fuel leaks, go to next step.
   
   If fuel is leaking, resolve the leak before continuing to the next step .

5. 5

   Have your helper to crank the engine while you observe the fuel pressure tester's gauge.

6. 6

   Your fuel pressure gauge will register one of the two following results:
   
   1.) The fuel pressure gauge will register the indicated fuel pressure specification
   
   2.) The fuel pressure gauge will NOT register the indicated fuel pressure specification.

OK, now that the testing part is done, let's take a look at what your results mean:

CASE 1: The fuel pressure gauge registered 0 PSI. This confirms that the cause of your engine's no-start problem is caused by a lack of fuel.

Now, I usually take two more precautions, before condemning the fuel pump as bad and this is to check:

1. That the fuel pump inertia switch isn't activated and cutting power to the fuel pump. For more info on this take a look at the next section: Checking The Fuel Pump Inertia Switch.
2. If the fuel pump inertia switch is OK, then I still make sure that the fuel pump is getting 12 Volts as the engine is cranking. This is just to make sure that the fuel pump relay and fuse are OK and doing their job.

To check that the fuel pump is getting power (after the inertia switch has been checked) you'll need to attach a multimeter in Volts DC mode to the wire that supplies this voltage to the fuel pump and while a helper cranks the engine, verify that the fuel pump is getting this power. If the 12 Volts are being supplied to the fuel pump, you have now 100% verified that the fuel pump is fried and needs to be replaced.

CASE 2: The fuel pressure gauge registered the correct fuel pressure specification. This fuel pressure gauge result lets you know that the fuel pump is working and delivering enough fuel to the fuel injectors.

The reason your 4.0L Ford vehicle is not starting is due to another reason. The fuel pump is OK. For more troubleshooting options, take a look at the following tutorial:

• How To Troubleshoot A No-Start Problem (4.0L Ford Explorer, Aerostar, And Mercury Mountaineer).