FUEL PUMP TEST 2: Using A Fuel Pressure Gauge
Testing the fuel pump's pressure is one of the most accurate ways to verify that the fuel pump is good or bad.
Ford has made it super easy to attach a fuel pressure gauge to the fuel system to test the fuel pump since there's a Schrader valve on the fuel rail (see image 1 of 2 in the image viewer).
If you don't own a fuel pressure gauge, I have made some recommendations at the end of the article on which fuel pressure gauge set to buy and where to buy it.
These are the test steps:
- 1
Connect the fuel pressure gauge to the Schrader valve on the fuel rail.
- 2
When ready, ask your helper to crank the engine while you observe the fuel pressure tester's gauge.
- 3
Your fuel pressure gauge will register one of the two following results:
1.) The fuel pressure gauge will register 35 PSI, or
2.) The fuel pressure gauge will register 0 PSI.
OK, now that the testing part is done, let's take a look at what your results mean:
CASE 1: If the fuel pressure gauge registered 0 PSI. This confirms that the cause of your F150's (Expedition, Crown Victoria, Thunderbird, Cougar, Grand Marquis, etc.) is caused by a lack of fuel.
This result usually means that the fuel pump is bad but not always. For example, you could have a blown fuel pump fuse, or a bad fuel pump relay or a fuel pump interrupt switch that has activated.
Taking into account the above conditions I've just mentioned and to make sure that the fuel pump is really the cause of this 0 PSI fuel pressure reading, you must verify that the fuel pump is getting power (12 Volts) when the engine is cranking (this is accomplished from underneath the vehicle, by tapping into the wire that feeds the fuel pump with power, with a multimeter).
CASE 2: If the fuel pressure gauge registered 35 PSI: This fuel pressure gauge result lets you know that the fuel pump is working and delivering enough fuel to the fuel injectors.
The cause of your Crown Victoria's (E150, Mustang, Town Car, Navigator, Thunderbird, etc.) no-start condition is caused by something else.
Location Of The Schrader Valve
The Schrader valve is always located on the fuel injector rail (on the vehicles covered by this tutorial). Generally on the passenger side of the engine.
Checking The Fuel Pump Inertia Switch
The fuel pump inertia switch is tasked with the job of cutting power (or ground) to the fuel pump in case of an impact, which causes the engine to stall (if it was running) or for the engine to crank but not start due to a lack of fuel.
Although it's designed to activate during a severe impact cause by an automobile accident, sometimes it gets activated by less than severe impacts (and this happens a lot).
This means that it's always a good idea to check and reset the inertia switch whenever testing the fuel pump. On the majority of the vehicles covered by this tutorial, the inertia switch is located below the right side of the instrument panel, behind the trim panel.
Resetting the fuel pump inertia switch simply involves pushing down on the button located on top of the inertia switch till it bottoms out. If the inertia switch has been jolted into shutting off the fuel pump, you'll feel a definite ‘click’ as you depress the button.
Related Test Articles
It's my mission to give you real world ‘how to test’ tutorials to help you to really test this or that on your 4.6L and 5.4L V8 Ford vehicle, so I've written several articles that may be of interest to you. You can find them here: Ford 4.6L, 5.4L Index Of Articles.
Here's a sample of the tutorials you'll find in the index:
- Troubleshooting P0172 And P0175 (Ford 4.6L, 5.4L).
- How To Test The Blower Motor (Ford 4.6L, 5.4L).
- How Can I Tell What's Wrong With My Transmission? (Ford 4.6L, 5.4L).
- How To Test Ford Coil-On-Plug Ignition Coils 4.6L and 5.4L V8 Engines (at: easyautodiagnostics.com).
- How To Test The Throttle Position Sensor Ford, Mercury, Lincoln 4.6L and 5.4L Engines (at: easyautodiagnostics.com).
- How To Test The FORD MAF 4.2L, 4.6L, 5.4L Round Air Filter Canister Assembly MAF Sensor (at: easyautodiagnostics.com).
- How To Test Ford MAF Sensors Using a Multimeter (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!
