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).
Contents of this tutorial:
- Symptoms Of A Bad Fuel Pump.
- Where To Buy A Fuel Pressure Gauge.
- TEST 1: Fuel Pressure Test With Gauge.
- TEST 2: Using Starting Fluid.
- Location Of The Fuel Pressure Schrader Valve Test Port.
- Checking The Fuel Pump Inertia Switch.
- Where To Buy The Fuel Pump And Save.
- More Ford 4.0L Ford Explorer And Aerostar Tutorials.
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
When a fuel pump fails, it usually happens in one of two main ways:
- Engine Won't Start: The fuel pump just stops working altogether and the engine won't start because it's not getting any fuel.
- Engine Starts, But Runs Rough: In this type of failure, the fuel pump is on its way out, but it still manages to push enough fuel to get the engine started. However, it's not pumping enough fuel for the engine to run smoothly, especially when it's under load (like when you're driving).
Some common symptoms that the fuel pump might be failing or already has failed include:
- Engine Won't Start: You turn the key, but instead of starting, the engine just cranks and cranks without actually starting up.
- Stalling Right After Starting: Sometimes, the engine might start up OK, but then it putters out and stalls after just a few seconds.
- Stalling When You Hit the Gas: The engine manages to start, but the moment you stick the transmission in Drive and hit the gas pedal to accelerate, it stalls out on you.
- Lack Of Power When Driving: You notice that your vehicle just doesn't have the power it used to, especially when you're driving and need to speed up or climb a hill.
- Backfiring: If you hear loud popping sounds coming from under the hood when you're pressing on the gas pedal, that could be a sign of the fuel pump not delivering enough fuel to the engine.
- Check Engine Light On: If the check engine light is on your dashboard and you're getting trouble codes like P0171 or P0174, which are all about the air-fuel mixture being off, then your fuel pump could be part of the problem.
I want to point out before moving on the next heading, that other components (when they fail) can also cause similar problems/symptoms and mimic a failing fuel pump.
That's why it's essential to check the fuel pump's pressure output with a fuel pressure gauge before deciding to replace it.
Where To Buy A Fuel Pressure Gauge
Owning a fuel pressure gauge is now becoming a must and it's an investment that will pay for itself many times over. 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. Here are my recommendations:
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
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
Install the Ford Schrader valve adapter on the Schrader valve.
- 3
Connect the fuel pressure gauge to the Schrader valve adapter.
- 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
Have your helper to crank the engine while you observe the fuel pressure tester's gauge.
- 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:
- 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.
- 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:
