How To Test The Fuel Pump (1994-1997 4.6L Crown Victoria, Grand Marquis)

Testing the fuel pump's pressure output with a fuel pressure test gauge is pretty much the best method to find out if its failing or has failed.

In this tutorial, I’ll explain how to perform the fuel pump pressure test and how to interpret your test results to see if the fuel pump is OK or if it's bad.

I'm also gonna explain how to use starting fluid to check if a lack of fuel is the reason the engine won't start.

APPLIES TO: This tutorial applies to the following vehicles:

• 4.6L Ford Crown Victoria: 1994, 1995, 1996, 1997.
• 4.6L Mercury Grand Marquis: 1994, 1995, 1996, 1997.

WIRING DIAGRAM: The following fuel pump circuit wiring diagram may come in handy:

• Fuel Pump Circuit Wiring Diagram (1996, 1997 4.6L Crown Victoria, Grand Marquis)

Common Symptoms Of A Bad Fuel Pump

When a fuel pump fails, it'll usually suffer one of two problems:

• Insufficient Pressure: The fuel pump may produce enough pressure to get the engine started, but not enough to keep the engine running (especially under load).
• Total Loss Of Pressure: In this case, the fuel pump ceases to function completely, delivering no fuel to the engine. This lack of fuel causes the engine to not start.

There's quite a few symptoms that you're gonna see when the fuel pump is starting to fail, the most common ones you're going to see:

• Engine No Start: The engine cranks but does not start.
• Stalling After Start: The engine starts but stalls after a few seconds.
• Stalling On Acceleration: The engine starts but as soon as you step on the accelerator pedal, the engine stalls.
• No Power Under Load: Lack of power while driving the vehicle.
• Backfiring: Explosions (loud popping sounds) can be heard coming from the intake manifold when you step on the accelerator while the engine is under load.
• Check Engine Light : The check engine light is on, and lean air-fuel mixture trouble codes are stored in the fuel injection computer's memory.

Before moving on, I wanna point out that other faulty ignition or fuel system components can cause engine performance issues that mimic a failing fuel pump. For this reason, you've got to check the fuel pump's pressure with a fuel pressure test gauge before deciding to replace it.

Where To Buy A Fuel Pressure Test Gauge

For anyone working on their own vehicle, a fuel pressure test gauge is a must-have tool. The cool thing is that you can buy one at almost any auto parts store. For testing the fuel pressure on your Ford Crown Victoria or Mercury Grand Marquis, the tester I use and recommend is the Actron CP7838 Professional Fuel Pressure Tester.

This fuel pressure test kit will connect to the fuel rail's Schrader valve, is durable, and doesn't cost an arm and a leg: Actron CP7838 Professional Fuel Pressure Tester.

All of the following fuel pressure test gauge kits will help test your Crown Vic or Grand Marquis' fuel pump:

Safety Precautions To Take When Testing The Fuel Pump Pressure

Before you start your tests, remember to play it safe to avoid any accidents or surprises. Here are a couple of important precautions to take:

• Work With A Cold Engine: Perform the fuel pump pressure test or the starting fluid test with the engine cold. This precaution reduces the likelihood of starting the engine on fire.
• Avoid Flames And Sparks: It's important to steer clear of any open flames, sparks, or potential ignition sources when working with gasoline or starting fluid. Remember, gasoline and starting fluid vapors are extremely flammable and can easily ignite, potentially causing fires or explosions.
• Wear Protective Gear: Wear safety glasses to protect your eyes from fuel splashes and gloves to prevent skin contact with gasoline or starting fluid.
• Have a Fire Extinguisher Nearby: Have a fire extinguisher nearby in case of an emergency. Make sure the fire extinguisher is rated for use with flammable liquids.
• Follow Fuel Pressure Gauge Manufacturer Instructions: When using a fuel pressure gauge to test the fuel pump's pressure, it's important to carefully follow the manufacturer's instructions. This ensures you're connecting the gauge properly, the testing procedure is performed safely, and that you'll obtain accurate fuel pressure readings.

By following these safety measures, you can minimize the risk of accidents and perform the fuel pressure check effectively and safely.

Fuel Pressure Specifications

The following fuel pressure specifications apply to the 1994-1997 4.6L Ford Crown Victoria and Mercury Grand Marquis:

Fuel Pressure With The Key On Engine Off
1994-1995	35-45 PSI.
1996-1997	30-45 PSI.

TEST 1: Testing The Fuel Pressure With A Fuel Pressure Test Gauge

Testing the fuel pump with a fuel pressure gauge is a piece of cake, thanks to Ford's 'generosity' of including a fuel pressure test port on the fuel injector rail (they don't do this anymore on newer models).

This test port, known as a Schrader valve, is located on the fuel injector rail that serves cylinders 1, 2, 3, and 4 (bank 1, on the passenger's side of the engine). The Schrader valve is where you'll connect your fuel pressure test gauge to.

If the fuel pump is bad, the fuel pressure gauge will generally register 0 PSI. On the other hand, if the fuel pump is working but not sending enough fuel to the fuel injectors, the pressure reading will be below the factory specifications.

IMPORTANT: If you haven't already done so, check the fuel pump inertia switch first. See: Fuel Pump Inertia Switch Check.

NOTE: You'll need a fuel pressure tester that can connect to the Schrader valve. If you don't have one, take a loot at my recommendations here: Where To Buy A Fuel Pressure Test Gauge.

These are the test steps:

1. 1

   Disconnect the ignition coil packs from their electrical connector.
   
   The fuel pump is tested with the key on engine off (KOEO) and disconnecting the ignition coils will keep the engine from starting.

2. 2

   Locate the Schrader valve on the fuel injector rail crossover line (see photos above).

3. 3

   Remove the dust cap from the Schrader valve and place a shop towel under the general area of the Schrader valve.
   
   NOTE: The shop towel's job is to absorb and fuel that may leak when performing step 3.

4. 4

   Connect your fuel pressure tester to the Schrader valve.

5. 5

   Have your helper crank the engine and then let go of the key while you observe the needle on the fuel pressure tester gauge.
   
   NOTE: What you want to do is crank the engine by turning the ignition key and then letting it go. The key should automatically stay in the ON position after you let go, and that’s exactly where we need it to be. Since the ignition coils are disconnected, the engine won't actually start up.

6. 6

   Your fuel pressure gauge should register the indicated fuel pressure specification.
   
   1994-1995: 35 to 45 PSI.
   
   1996-1997: 30 to 45 PSI.

Let's examine your test results:

CASE 1: The fuel pressure is within the indicated specification. This is the correct test result.

This test result confirms that the fuel pump in your Crown Vic (Grand Marquis) is OK (functioning correctly).

CASE 2: You got 0 PSI fuel pressure. This test result lets you know that the fuel pump is defective and is causing the engine to not start.

Before you replace a fuel pump make sure that the fuel pump relay and fuel pump fuse are supplying power to the fuel pump when the engine is being cranked.

If battery power is available to the fuel pump, when cranking the engine, then you can confidently conclude that the fuel pump is defective and that it needs to be replaced.

CASE 3: The fuel pressure was below the indicated fuel pressure specification. This test result lets you know that even though the fuel pump is supplying some fuel it's not supplying enough to have the engine run optimally.

This is an indication that the fuel pump is failing and needs to be replaced.

Using Starting Fluid To Diagnose A No-Start Condition

One of the quickest methods to see if a lack of fuel is causing the engine to not start (you know, because of a bad fuel pump) is using starting fluid.

The starting fluid test involves spraying starting fluid into the intake manifold throttle body's bore, then having someone crank the engine.

If the engine starts and runs briefly, you now know that the engine isn't getting fuel. Now, if the engine doesn't start, then the problem isn't related to fuel supply.

It's important to note that if the engine no-start problem is indeed caused by a lack of fuel, the engine will run only for a few seconds. This is because it's only running on the starting fluid you sprayed, and once that gets consumed, the engine will turn off.

IMPORTANT: To achieve the most accurate result from your starting fluid test, make sure all 8 cylinders are getting spark. If you haven't checked for spark yet, do so before proceeding with the starting fluid test.

CAUTION: As a safety precaution, you should never spray starting fluid into the throttle body while the engine is cranking. Instead, you should first spray starting fluid into the throttle body and then crank the engine.

These are the test steps:

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 step 2.

2. 2

   Spray starting fluid down the bore of the throttle body.
   
   After spraying a good squirt of starting fluid, quickly reconnect the air duct to the throttle body (you don't have to tighten the hose clamp)

3. 3

   Have your helper crank the engine once the intake air duct is back on the throttle body.

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

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

CASE 1: The engine did not start, not even a few seconds. This test result tells you that a lack of fuel from the fuel pump IS NOT causing the engine's no-start problem.

I want to point out that this conclusion is true only if all spark plug wires are sparking.

CASE 2: The engine started but died after a few seconds. This test result tells you that the engine's no-start problem is caused by a lack of fuel.

Fuel Pump Inertia Switch Check

Your Crown Vic (Grand Marquis) comes equipped with a fuel pump inertia switch, which you can find on the left side of the trunk. Its job is to cut power to the fuel pump in the event of an impact.

If your Crown Vic or Grand Marquis' fuel pump inertia switch gets activated, it'll prevent the engine from starting or cause it to stall by cutting off the fuel supply to it.

Although the fuel pump inertia switch is designed to primarily activate when your vehicle suffers a significant impact, like in a car crash, it's sensitive enough to be triggered by minor bumps as well.

Given that even a slight jolt can activate the switch, it's important that you check and reset it (if necessary) as a routine step when troubleshooting any fuel pump issue or engine no-start problem.

To reset the fuel pump inertia switch, just press firmly down on the button located at the top of it until you hear a click. The click tells you it's reset and that it'll allow power to flow to the fuel pump.

More 4.6L Crown Victoria And Grand Marquis Tutorials

If this tutorial was helpful, be sure and take a look at all of the 4.6L Ford Crown Vic and Mercury Grand Marquis diagnostic tutorials and wiring diagrams in this index:

• 4.6L Crown Victoria And Grand Marquis Index of Articles.

Here's a sample of the tutorials you'll find there:

• How To Test Engine Compression (1992-2011 4.6L Crown Victoria, Grand Marquis).
• Blown Head Gasket Tests (1992-2011 4.6L Crown Victoria, Grand Marquis).
• How To Test The Fuel Injectors (1992-1997 4.6L Crown Victoria, Grand Marquis).