How To Test The Ford Fuel Pump Relay -No Start Troubleshooting (Green Relay)

TEST 2: Checking For Power (High Current Circuit)

So far, you have checked and confirmed that the low current circuit of the fuel pump relay is getting power (TEST 1).

The next step, in troubleshooting the fuel pump relay, is to make sure that it's getting battery power on wire labeled with the number 4.

This wire is the one that supplies power to the Ford fuel pump relay's high current circuit.

OK, to get this test going, this is what you'll need to do:

1. Place your multimeter in Volts DC mode.
2. With the red multimeter test lead, probe the wire labeled with the number 4.
   • This is where a wire piercing probe comes in handy (to see what this tool looks like, click here: Wire Piercing Probe).
   • NOTE: It's not a good idea to probe the front of the fuel pump relay connector, since the metal female terminal could get damaged.
3. Ground the black multimeter test lead directly on the battery negative (-) terminal or on a clean metal spot on the engine.
4. Turn the key to the ON position.
5. Your multimeter should register one of two things:
   • Battery voltage (10 to 12 Volts DC).
   • Or no voltage at all.
6. When done, turn the key to the OFF position.

OK, let's interpret your test results:

CASE 1: Your multimeter showed battery power. This is the normal and expected test result and it confirms that the high current circuit (that feeds the fuel pump itself with power) is being fed power.

The next step is to jumper wires number 3 and number 4 of the fuel pump relay connector to manually get the fuel pump to come on. Go to: TEST 3: Jumpering The Fuel Pump Circuit.

CASE 2: Your multimeter DID NOT show battery power. Recheck all of your multimeter connections and repeat the test one more time.

If the multimeter still does not register battery voltage (10 to 12 Volts DC) this second or third time around, then you need to find out why this voltage is missing.

These 10 to 12 Volts are provided by the ignition switch (with the key ON or engine cranking), and if they are missing, the fuel pump relay will not activate the fuel pump.

TEST 3: Jumpering The Fuel Pump Circuit

OK, so far you have confirmed that the fuel pump relay on your Ford car or pickup is getting power on wires labeled with the numbers 2 and 4.

In this test step, we're gonna' jumper two wires (numbers 3 and 4) together to manually get the fuel pump to activate.

Although it's not absolutely necessary, you should connect a fuel pressure gauge to the Schrader valve (on the fuel injector fuel rail), so that when you jumper the fuel pump to power, you can check that the fuel pressure the fuel pump is outputting is enough to start your vehicle.

If you're in need to a fuel pressure gauge, I recommend this one:

Actron CP7838 Professional Fuel Pressure Tester.

This fuel pressure gauge is inexpensive (compared to how much you'll pay for one at your local auto parts store), and has the adapter to test the fuel pressure on your Ford car and/or pickup.

OK, to get this test going, this is what you'll need to do:

1. Connect your fuel pressure gauge to the Schrader valve on the fuel rail.
2. Disconnect the fuel pump relay from its connector.
3. Locate the terminals labeled with the numbers 3 and 4.
4. Using a jumper wire, jumper terminals 3 and 4 together.
   • NOTE: Don't use anything that is too big to fit into the female terminals of the connector, OR you run the risk of damaging the metal terminals.
   • By 'damaging', I mean that the female terminals will open up permanently and later cause a false contact that will become a headache later to troubleshoot.
5. Turn the key to the ON position (but don't crank the engine).
6. You should hear the hum of the fuel pump (as it's activated) AND you should see the fuel pressure rise on your fuel pressure gauge.
   • Fuel pressure should be between 35 to 45 PSI.

OK, let's interpret your test results:

CASE 1: Fuel pump came on and the fuel pressure was at specification (35 - 45 PSI). This tells you that the fuel pump is OK.

This test result indirectly tells you several things also:

• That the fuel pump inertia switch is OK (not tripped).
• That the wiring between the fuel pump and the fuel pump relay is OK.

The next step is to make sure that the EEC computer (fuel injection computer) is activating the fuel pump. For this test, go to: TEST 4: Checking That The Computer Is Activating The Fuel Pump Relay.

CASE 2: Fuel pump came on but the fuel pressure WAS NOT at specification (35-45 PSI). This tells you that the fuel pump is getting power but that it's bad and needs to be replaced.

To be a little more specific: you ca hear the fuel pump come on if you place your ear on the fuel tank filler tube, but the fuel pressure does not register any fuel pressure or the fuel pressure is way below the 35 PSI minimum.

CASE 3: Fuel pump DID NOT come on and the fuel pressure WAS NOT at specification. This test result means one of two things:

• That the fuel pump is bad.
  • To further check this, you'll need to confirm that the fuel pump inertia switch has not tripped by pushing down on its button and resetting it.
  • Or, checking for 10 to12 Volts at the fuel pump connector itself (by the gas tank). NOTE: Checking that power (10 to 12 Volts) are actually reaching the fuel pump is a very important step before replacing it.
• The fuel pump inertia switch has been tripped and is not allowing current to reach the fuel pump.
  • To check this, locate the fuel pump inertia switch and push down on its button. If the inertia switch has tripped, you'll hear (and feel) a clicking sound when pushing down on the reset button. It if hasn't tripped, then you won't hear (or feel) anything when pushing down on its reset button.

TEST 4: Checking That The Computer Is Activating The Fuel Pump Relay

As you may already be aware, it's the fuel injection computer that activates the low current circuit of the fuel pump relay.

It does this by Grounding the circuit internally (inside the computer itself) and this can be easily verified with a 12 Volt automotive test light (or a multimeter).

There are some very important precautions you have to take and keep in mind when testing this circuit and they are:

• Never apply 12 Volts to this circuit (either intentionally or accidentally), or you'll fry the computer.
• Never jumper circuit numbers 1 and 2 together, or you'll fry the computer.
• This test step has to be done with the engine cranking, so you have to be careful!

OK, to get this test going, this is what you'll need to do:

1. Unplug the fuel pump relay from its connector.
2. Connect your 12 Volt test light's alligator clip to the battery's positive (+) terminal.
3. With the metal probe point of the test light, probe the wire identified with the number 1.
   • What I recommend you do is to probe behind the fuel pump relay connector or probe the wire itself.
   • Avoid probing the front of the fuel pump relay connector to avoid damaging the female terminal.
4. Have a helper crank the engine for you as you observe the test light.
   • IMPORTANT: Take all necessary safety precautions and think safety when working around a cranking engine.
5. As long as the engine is cranking, the 12 Volt test light should come ON and stayed ON.
6. When done, turn the key to the OFF position.
   • With the key OFF (or out of the ignition switch), the 12 Volt test light should turn OFF.

OK, let's interpret your test results:

CASE 1: The 12 Volt test light came ON and stayed ON the whole time the engine was cranking. This is the normal and expected test result and it confirms that the fuel injection computer (EEC Electronic Control Module) is activating the fuel pump relay.

So far, if you started testing from the beginning, you have checked and confirmed that:

1. The fuel pump relay's low current circuit (wire 2) is getting power (TEST 1).
2. The fuel pump relay's high current circuit (wire 4) is getting power (TEST 2).
3. That the fuel pump does come on and is producing the correct fuel pressure specification (35 to 45 PSI) (TEST 3).
4. In this test, (TEST 4), you have confirmed that the computer is Grounding the relay's low current circuit.

The next step is to check that the fuel pump relay is sending power to the fuel pump. For this test, go to: TEST 5: Testing The Fuel Pump Voltage Output At The Relay.

I also recommend taking a look at: TEST 6: Fuel Pump Stays On All Of The Time.

CASE 2: The 12 Volt test light DID NOT come ON. Make sure that you're probing the correct wire and repeat the test one more time.

If your 12 Volt automotive test light still does not come ON, then the PCM is not activating the fuel pump relay. I can tell you that it's extremely rare for the fuel injection computer to go bad and not activate the fuel pump relay (but I'm sure it happens).

The most likely problems causing this missing voltage are:

1. An 'open-circuit' problem between the fuel injection computer (EEC Electronic Control Module) and the fuel pump relay connector.
2. The PIP (Profile Ignition Pickup -which is the crankshaft position sensor inside the distributor) is bad and not sending a PIP signal (crankshaft position position signal) to the fuel injection computer.
   • When this happens (a bad PIP sensor), you'll also notice that there's NO SPARK at any spark plug wire.
   • The ignition coil won't be sparking either.