How to Diagnose a Failing Fuel Pump

The fuel pump is an important part of the fuel system. It is located either inside the fuel tank on newer cars or just outside of the fuel tank on older cars. The fuel pump is responsible for pushing fuel towards the engine.

Like all moving car parts, a fuel pump can eventually fail. Do you suspect that your fuel pump isn’t working as well as it should? You should officially diagnose the problem and get it replaced (if needed) as soon as possible.

Symptoms to Look For

It’s important to catch a failing fuel pump early on because a weak fuel pump can cause many different performance problems. If you experience most or all of the following symptoms, then there’s a good chance your fuel pump is on the verge of death.

• Engine lacks power at high speeds.
• Hard starting, or not starting at all.
• Loud whine from the gas tank.
• Loss of power when driving uphill or towing.

If your engine refuses to start, then your fuel pump may have completely failed. It’s because the pump isn’t pumping any fuel to the engine to enable combustion. In this case, you will need to replace your fuel pump ASAP.

Confirming the Issue

Assuming the car will still run, but has performance issues, the following steps will help assess the fuel pump.:

1. Refer to a shop manual to see fuel pressure specifications at idle and under load.
2. Connect the fuel pressure gauge. The shop manual will show where it connects. Generally, it will connect in one of two locations:
   1. A fuel pressure test port.
   2. In place of the fuel filter.
3. Check the pressure while idling and under load.

If the pump doesn't generate the pressure stated in the shop manual, then the fuel pump is underperforming and you’ll need to get it replaced.

You can also perform an electrical test to see if the pump is underperforming due to an electrical issue like a bad connection or low voltage. To do this:

1. Inspect the wiring between the fuel pump and relay to make sure there are no loose or corroded connections.
2. Test the relay to make sure it works properly.
3. Connect a voltmeter to the fuel pump’s positive and negative terminals.
4. The voltage at the fuel pump should be very close to the voltage measured at the starting battery.
5. If there is more than a half a volt drop, the wiring to the pump has too much resistance. This is usually caused by a loose connection or a corroded connection.

Finding the Right OEM Replacement Fuel Pump For Your Ford

If you’ve determined that your fuel pump is bad, then you’ll need to replace it as soon as possible. The good news is that you can easily find the right genuine OEM fuel pump assembly by looking up your vehicle in our catalog. You can also see if your Ford is in this list of our top selling fuel pump assemblies:

• Part No. YW4Z-9275-BC: For 2000-2005 Thunderbird and Lincoln LS models
• Part No. XL3Z-9H307-DB: For 1999-2004 F-150 and F-250 models
• Part No. F85Z-9H307-AB: For 1997-1998 F-150 and F-250 models
• Part No. F6TZ-9A407-CC: For 1992-1997 Bronco, F-150, F-250, and F-350 models
• Part No. 8L3Z-9H307-B: For 2004-2008 F-150 and Lincoln Mark LT models