Testing the Ford fuel pump relay on the car is not hard to do.
With the help of this 'How To' tutorial, I'll show you how to do it using only a multimeter.
You'll be able to find out if the fuel pump relay, or the fuel pump inertia switch, or the fuel pump is the cause of the no-start condition on your Ford car or pickup.
If your fuel injected Ford pickup, van, or car still has the Ford relay, this bad boy will be a green color (like the one in the image above). If it has already been replaced with an after-market one, this relay won't be green, but will have a gray body.
Contents of this tutorial:
- What Tools Do I Need To Test The Relay?
- Fuel Pump Relay Circuit Descriptions.
- Relay Basics: How The Fuel Pump Relay Works.
- Where To Buy The Fuel Pump Relay.
- TEST 1: Checking For Power (Low Current Circuit).
- TEST 2: Checking For Power (High Current Circuit).
- TEST 3: Jumpering The Fuel Pump Circuit.
- TEST 4: Checking That The Computer Is Activating The Fuel Pump Relay.
- TEST 5: Testing The Fuel Pump Voltage Output At The Relay.
- TEST 6: Fuel Pump Stays On All Of The Time.
- Ford Fuel Pump Relay Test Summary.
- Where To Buy A Fuel Pressure Gauge.
You can find this tutorial in Spanish here: Cómo Probar El Relé De La Bomba De Gasolina (Relé Verde) (at: autotecnico-online.com).
The following tutorial may be of help: How To Test The Fuel Pump (Ford 4.9L, 5.0L, 5.8L) (at: troubleshootmyvehicle.com).
For your cross reference information:
- AutoZone part #:
- Duralast 19911.
- O'Reilly part #:
- BWD R647.
- Master Pro Ignition 2DR-1039.
- Others:
- STANDARD MOTOR PRODUCTS Part # RY46T.
- STANDARD MOTOR PRODUCTS Part # RY46.
- ORIGINAL ENGINE MANAGEMENT Part # DR1039.
- AIRTEX / WELLS Part # 1R1294.
What Tools Do I Need To Test The Relay?
You need a few basic things and they are:
- Multimeter
- A digital or analog multimeter will work.
- If you need to buy one or are looking to upgrade, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
- Wire piercing probe
- This tool is a time saver of the first order. To see what this tool looks like, click here: Wire Piercing Probe.
- Jumper wires
- You'll need two of them with alligator clips on both ends (you can make these yourself).
Fuel Pump Relay Circuit Descriptions
The Ford fuel pump relay has 4 wires that connect to it.
Each wire has a specific job to do and these are their circuit descriptions:
IMPORTANT: Your specific Ford vehicle may not have the exact same colors listed below. This is no big deal, since the circuit descriptions are the same. You will be able to use the info in this article to diagnose the fuel pump relay on your Ford vehicle even if the colors of the fuel pump relay connector's wires are different!
| Ford Fuel Pump Circuits | ||
|---|---|---|
| Pin | Wire Color | Description |
| 1 | Tan w/ Green stripe * | Fuel Pump Relay Control |
| 2 | Red * | Power (from EEC Power Relay) |
| 3 | Brown * | Fuel Pump Output |
| 4 | Yellow * | Ignition Fused Power (Fuel Pump Fuse) |
* Your specific Ford vehicle may have different colors.
Relay Basics: How The Fuel Pump Relay Works
The core purpose of a relay is to control a high amount of current with a smaller (lower) current. How? You might ask.
Well, every Ford fuel pump relay has two basic circuits and for the purpose of our discussion, we'll call them:
- A high current circuit.
- A low current circuit.
Both of these are completely independent from one another, in other words, voltage/current flowing thru' these circuits don't mix.
The high current circuit is the one that delivers the voltage (and thus current) to the fuel pump in the gas tank (or on the frame rail).
When the fuel pump relay is off (not activating the fuel pump), the high current circuit is 'open'.
In it's 'open' state current does not get sent to the fuel pump.
The low current circuit is the control circuit that 'closes' or 'opens' the high current circuit. By 'closing' the high current circuit, I specifically mean allowing voltage to pass thru' the relay (internally) and on its way to the fuel pump.
To get into more specifics, this is what happens when you turn the key and crank the engine:
- Power (in the form of 10 to 12 Volts) is applied to circuit 2.
- This voltage comes from the EEC Power relay.
- Power (in the form of 10 to 12 Volts) is applied to circuit 4.
- This voltage comes from the ignition switch.
- The fuel injection computer then Grounds circuit 1.
- This activates the fuel pump relay to pass current from circuit 4 to circuit 3.
- Circuit 3 is the one connecting to the fuel pump (via the inertia switch) and delivers the voltage/current it needs to activate.
- Before this voltage reaches the fuel pump, it has to go through the fuel pump inertia switch first.
- If the inertia switch has been tripped, it will 'open' the circuit and the voltage will not reach the fuel pump.
As you can see, there's really nothing complicated happening behind the scenes with the fuel pump relay and the way it activates the fuel pump when you turn the key ON and start cranking the engine.
OK, working theory lesson is over, let's get testing in the next page.
Where To Buy The Fuel Pump Relay
The following aftermarket relays are the replacement for the green fuel pump relay:
24%
TEST 1: Checking For Power (Low Current Circuit)
The very first thing you and I need to do is make sure the fuel pump relay is getting power.
This power is in the form of battery voltage and will range between 10 to 12 Volts DC.
Power is supplied to two circuits (wires). These two wires are the ones labeled with the number 2 and the number 4.
In this test, we'll focus on testing wire number 2 first (this wire is the one that feeds power to the low current circuit).
OK, to get this test going, this is what you'll need to do:
- Expose the fuel pump relays' 4 wires
- These 4 wires are usually wrapped in black electrical tape.
- Locate the wire that corresponds to circuit number 2.
- Set your multimeter in Volts DC mode and:
- With an appropriate tool (like a Wire Piercing Probe), pierce the wire labeled with the number 2 (in the image above) with the red multimeter test lead.
- NOTE: It's not possible to probe the front of the connector or you run the risk of damaging the metal female connector inside.
- Ground the black multimeter test lead directly on the battery negative (-) terminal or on a clean metal spot on the engine.
- Turn the key to the ON position.
- Your multimeter should register one of two things:
- Battery voltage (10 to 12 Volts DC).
- Or no voltage at all.
- When done, turn the key to the OFF position.
OK, let's interpret your test results:
CASE 1: Your multimeter showed battery power. This tells you the low current circuit of the fuel pump relay is getting juice and this is a good thing.
The next step is to verify that the fuel pump relay's high current circuit is being fed with battery power too. Go to: TEST 2: Checking For Power (High Current 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 (this voltage is provided by the EEC Power Relay).
- To test the EEC Power Relay, you'll find the tutorial here: Ford EEC Power Relay Test.
Without voltage in this wire (with the key ON or engine cranking), the fuel pump relay will not activate the fuel pump.
