How To Test The Fuel Pump (2005-2008 3.0L V6 Ford Escape, Mercury Mariner)

In this tutorial, I'm going to explain how to test the fuel pump pressure on the 2005–2008 3.0L V6 Ford Escape and Mercury Mariner (which use a returnless fuel system).

You can check the fuel pump pressure in one of two ways. One is by using a scan tool to look at the fuel rail pressure (FRP) sensor PID in live data and checking the pump's pressure output that way.

The other (and the way I'm gonna show you in this tutorial) is by connecting a mechanical fuel pressure gauge to the fuel rail and checking fuel pressure the old-school way.

Since these models don't have a Schrader valve on the fuel injector rail, I'll show you how to hook up a gauge and what adapter/fitting you'll need. Let me tell you, it's not hard.

I'm also going to show you how to do a starting fluid test to confirm if an engine no-start is being caused by a fuel delivery problem.

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

APPLIES TO: This tutorial applies to the following vehicles:

• 3.0L V6 Ford Escape: 2005, 2006, 2007, 2008.
• 3.0L V6 Mercury Mariner: 2005, 2006, 2007, 2008.
• 3.0L V6 Mazda Tribute: 2005, 2006.

FUEL PUMP DRIVER MODULE (FPDM) TESTS:

• FPDM Basic Operating Theory (2005-2008 3.0L Ford Escape, Mercury Mariner).
• Fuel Pump Driver Module Tests (2005-2008 3.0L V6 Ford Escape, Mercury Mariner).

Symptoms Of A Bad Fuel Pump

From my experience, fuel pumps usually fail in one of two ways:

• The pump stops working completely —no fuel reaches the injectors, and the engine cranks but won't start.
• The pump still runs but is failing —it delivers just enough fuel to get the engine started, but once you put it in Drive and step on the gas, the engine stalls or runs really rough.

When the fuel pump is weak and not sending enough fuel to keep the engine running right, you'll often see one or more of these problems:

• Engine won't start.
• Engine starts but then dies.
• Engine stalls under load (even just putting it in Drive and giving it gas).
• Lack of power when driving.
• Popping sounds from the intake manifold —these are backfires caused by a lean air/fuel mixture.
• Lean air/fuel mixture trouble codes (P0171, P0174) getting set in the PCM's memory and lighting up the check engine light.

Where To Buy A Fuel Pressure Gauge

Before you buy a fuel pressure test gauge, keep in mind that the 2005–2008 Ford Escape and Mercury Mariner don't come with a fuel pressure test port (Schrader valve) like the older models did. But you can still check fuel pressure —you'll just need a special adapter.

This adapter is called a hair-pin T-fitting, and many fuel pressure test kits already include it. They're not expensive, and they'll let you hook up a gauge to the fuel rail and get an accurate pressure reading.

The following fuel pressure test kits (links below) all include the T-fitting you'll need to connect the gauge to the fuel injector rail and check fuel pressure:

TEST 1: Checking Fuel Pressure With A Gauge

The Ford repair manual says to activate the fuel pump with a bi-directional scan tool when checking fuel pressure with a gauge. If you have one, that's great —you can use it to turn on the pump and check its fuel pressure output.

If you don't have a bi-directional scan tool, no problem. You can still check fuel pressure, and I'll explain how to do it step by step in the instructions below.

Here's the fuel pressure specification (2005-2008 3.0L V6 Escape/Mariner):

• KOER (Key On Engine Running): 39 PSI.
• KOEO (Key On Engine Off): 39 PSI.

One more thing: these test steps apply whether your Ford Escape or Mercury Mariner starts and runs, or whether it's dealing with a no-start condition.

IMPORTANT: Before checking fuel pressure, make sure the fuel pump inertia switch hasn't tripped. If it has, the fuel pump won't get power and the test results will be misleading. So double-check that first.

SAFETY FIRST: Always take the necessary safety steps when working with fuel. Work in a well-ventilated area, keep open flames and sparks far away, wear eye protection, and have a fire extinguisher nearby —just in case.

Alright, here's how to check fuel pressure, step by step:

1. 1

   Release the fuel pressure in the fuel line.
   
   See this section for the procedure: Fuel Pressure Release Procedure.

2. 2

   Connect your fuel pressure gauge.
   
   Disconnect the fuel supply line from the fuel injector rail and install the T-fitting (see the image above). Be sure and follow your test kit's instructions to avoid any complications.

3. 3

   Have your helper cycle the key ON and OFF several times —but don't crank the engine.
   
   This will prime the system. Watch closely for leaks.
   
   If everything stays dry, you're good to go.
   
   If you see or smell fuel, stop and fix the leak before continuing.

Scan Tool Pump Activation: Engine starts or doesn't start

1. 4

   Connect your bidirectional scan tool to the OBD II diagnostic connector.

2. 5

   Turn the key ON but don't start the engine.
   
   NOTE: The fuel pump activation (with the bidirectional scan tool) is done with the engine OFF.

3. 6

   Enter component tests and activate the fuel pump.
   
   NOTE: Consult your scan tool's user manual for exact steps on how to access the fuel pump activation feature —the process can vary depending on the brand and model.

4. 7

   The fuel pressure gauge should show 39 PSI.

Key On Engine Off (KOEO) Test (No Scan Tool): Engine doesn't start

1. 4

   Have your helper crank the engine, then release the key.
   
   NOTE: After cranking, the key should stay in the RUN position. If your helper turns it all the way to OFF, the test won't work —you'll need to do it again.

2. 5

   The fuel pressure gauge should show 39 PSI.

Key On Engine Running (KOER) Test (No Scan Tool): Engine starts and stays running

1. 4

   Have your helper start the engine and let it idle.

2. 5

   The fuel pressure gauge should show 39 PSI.

Let's break down what those results actually tell you:

CASE 1: The gauge reads 0 PSI. That means no fuel is getting to the injectors —which explains why the engine won't start.

Since the 2005-2008 Escape (Mariner) use a Fuel Pump Driver Module (FPDM), we can't rush to call the fuel pump bad just yet. Your next step is to test the FPDM module:

• Fuel Pump Driver Module Tests (2005-2008 3.0L V6 Ford Escape, Mercury Mariner).

CASE 2: Fuel pressure is lower than spec. If there are no FPDM or fuel rail pressure (FRP) sensor diagnostic trouble codes present, then this low fuel pressure test result tells you that the fuel pump is failing and needs to be replaced.

CASE 3: Fuel pressure is within spec. That's good —your fuel pump is working like it should.

If the engine still isn't starting, then you've got something else going on —but at least now you can cross the pump off your list.

TEST 2: Using Starting Fluid To Confirm A Fuel Delivery Problem

When I first started working on cars years ago, one of the very first things I was taught was to use starting fluid to see if a no-start was being caused by a lack of fuel. Back then, most cars had carburetors, but the same basic test applies to any fuel-injected engine —including the Ford Escape and Mercury Mariner.

The test is simple: spray starting fluid into the throttle body and crank the engine. If it starts, even for just a moment, that tells you the no-start is fuel-related. The engine will only run as long as the starting fluid is being consumed, so once it burns off, the engine will stall again.

I do want to point out that this isn't a precise way to confirm a bad fuel pump. You may still need to check fuel pressure with a gauge. But the result of the starting fluid test will point you in the right direction and help you decide what to do next.

Before you do the starting fluid test, make sure the engine has spark. On the 3.0L V6 Ford Escape/Mariner, the easiest way to do this is to check the ignition coils for cylinders 2, 4, and 6 (the three coils facing the radiator).

NOTE: If you haven't checked the inertia switch yet, do so now. If it's been tripped, the fuel pump won't run at all. You can find the steps here: Checking The Fuel Pump Inertia Switch.

Time to get your hands dirty:

1. 1

   Pull the intake duct off the throttle body. You don't need to remove it completely —just loosen it enough to spray fluid into the intake.

2. 2

   Manually open the throttle blade and give it a solid spray of starting fluid right into the intake manifold.

3. 3

   Reconnect the intake duct right after spraying. No need to tighten the clamp for now.
   
   IMPORTANT: Always reattach the duct before cranking as a safety precaution —in case of a backfire through the intake.

4. 4

   Now have your helper crank the engine while you observe what happens.

5. 5

   Here's what you're looking for:
   
   1.) The engine starts for a moment, then stalls.
   
   2.) The engine just cranks and never fires.

Let's go over what each result means:

CASE 1: It started, then shut off. Since the engine is getting spark —but not fuel, it started with the starting fluid you sprayed into the throttle body bore.

Most of the time, that points to a bad or non-functioning fuel pump. I still recommend confirming it with an actual fuel pressure test: TEST 1: Checking Fuel Pressure With A Gauge.

CASE 2: It didn't start at all. If the engine doesn't fire with starting fluid (and you've confirmed that all spark plug wires are sparking), the issue isn't fuel-related.

That said, this test isn't always 100% conclusive. If in doubt, go ahead and run a fuel pressure test to rule it out for good: TEST 1: Checking Fuel Pressure With A Gauge.

Checking The Fuel Pump Inertia Switch

The 2005-2008 Ford Escape and Mercury Mariner come equipped with a fuel pump inertia switch, located on the passenger side kick panel —right under the glove box, near the floorboard.

This switch is designed to cut power to the fuel pump in the event of an impact, like a car crash. When it's tripped, the fuel pump is shut off so that if a fuel line is damaged, fuel won't be sprayed everywhere. It's an important safety device.

The thing is, it doesn't take a crash to trip it. Even a hard bump —like hitting a curb while parking, driving over a big pothole, or slamming the door too hard— can set it off. When that happens, the engine won't start because the fuel pump isn't delivering fuel to the injectors.

That's why, before checking fuel pressure with a gauge, it's always a good idea to make sure the inertia switch hasn't tripped. Resetting it is simple: just press the large red button on top of the switch until it bottoms out. If it was tripped, you'll feel and hear a distinct click as it resets.

If the switch was the issue, once you reset it the engine should crank and start right up, with no further testing required. If the switch wasn't tripped, then go ahead and move on to checking fuel pump pressure with a gauge.

If you do need to test the inertia switch, this tutorial will help you with the test:

• Fuel Pump Inertia Switch Tests (2001-2012 3.0L V6 Ford Escape, Mercury Mariner).

Fuel Pressure Release Procedure

The fuel system on your Ford Escape or Mercury Mariner may be under pressure, and the last thing you want is to disconnect the fuel supply line from the injector rail and have fuel spray everywhere. That's not only messy —it's a serious safety hazard.

The good news is we can safely relieve fuel pressure before disconnecting anything, and that's exactly what I'm going to show you how to do in this section.

The step-by-step instructions below explain the fuel pressure release procedure for the 2005–2008 3.0L V6 Ford Escape and Mercury Mariner:

1. Remove the fuel pump fuse:
   • 2005–2007: Fuse 6 (in the Battery Junction Box).
   • 2008: Fuse 4 (in the Battery Junction Box).
2. Crank the engine. If it starts, let it run until it stalls on its own.
3. Crank the engine a few more times —until it stops firing completely.
4. Wrap a shop towel around the fuel line and disconnect it from the injector rail.
   • The towel will help catch any leftover fuel in the line.
5. Reinstall the fuel pump fuse once the line is disconnected.
6. After completing the pressure test, clear any diagnostic trouble codes that may have set while cranking the engine with the fuel pump disabled.

More 3.0L V6 Ford Escape Diagnostic Tutorials

You can find a complete list of 3.0L V6 Ford Escape, Mercury Mariner, and Mazda Tribute diagnostic tutorials in this index:

• 3.0L V6 Ford Escape Index Of Articles.

Here's a sample of the diagnostic tutorials you'll find in the index:

• How To Test The MAF Sensor (2001-2007 Ford 3.0L V6 Ford Escape).
• How To Test Engine Compression (2001-2012 3.0L V6 Ford Escape).
• How To Test For A Blown Head Gasket (2001-2012 3.0L V6 Ford Escape).
• How To Test The Fuel Pump (2001-2004 3.0L Ford Escape).