Testing the Ford fuel pump relay on the car is not that 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 viewer). If it has already been replaced with an after-market one, this relay won't be green, but will have a gray body.
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
- STANDARD MOTOR PRODUCTS Part # RY46T
- STANDARD MOTOR PRODUCTS Part # RY46
- ORIGINAL ENGINE MANAGEMENT Part # DR1039
- AIRTEX / WELLS Part # 1R1294
You can find this tutorial in Spanish here: Cómo Probar El Relé De La Bomba De Gasolina (Relé Verde) (at: autotecnico-online.com).
What Tools Do I Need To Test The Relay?
You need a few basic things and they are:
- 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|
|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 happpens when you turn On 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 that runs 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.