When you order a fuel pump for your vehicle, you may be surprised to see it in a huge box. That is because you must replace the entire fuel pump module or hanger instead of just the fuel pump. Some units are “open” so you can see the pump, sock, filter and wiring; and some of “closed” so you see a large plastic cylinder.
Fuel Pump Dissection
The actual fuel pump is a cylindrical metal tube that contains several parts. Chances are, you’ll never see the inside of a fuel pump, but knowing what it contains may help you understand how a fuel pump could malfunction. Most fuel pumps contain the following:
Fuel Pump Modules
When purchasing a fuel pump and you are quoted for the price of an entire unit, you most likely cannot replace the pump itself. Some manufacturers will sell the entire unit or just the pump itself, but keep in mind that other parts of the unit do malfunction and wear over time and it might save you money in the long run to replace the entire unit.
A fuel pump module usually consists of the following basic parts:
- Wiring: The wiring at the top is the fuel pump positive wire, negative wire, the sender positive wire and the sender negative wire. The wires are usually connected from the fuel pump unit to the wiring harness via a harness plug.
- Fuel Supply Line: The fuel supply line runs from the fuel pump to the fuel module outlet.
- Fuel Return Line: This line allows unused fuel to return to the fuel tank. Not all fuel pumps use a return system.
- Fuel Level Sender: This is the part of the fuel pump that tells you how much fuel you have in the tank. The sender reads the position of the float and sends the information to the fuel gauge. If the float is broken or the float’s arm is bent, the fuel gauge will not read properly.
- Fuel Pump: The fuel pump itself is located. Inside of the fuel pump module.
- Sock: The sock is a filter located at the bottom of the fuel pump. It strains most debris that may be sitting at the bottom of the fuel tank before it reaches the pump and fuel lines.
Any one of these parts may malfunction and cause your fuel pump not to work at all, to work intermittently or to work but provide the wrong pressure for your vehicle. If you don’t have the proper fuel pressure, if your vehicle runs at all, it will run poorly, as fuel injectors require a certain pressure -- commonly between 40 to 60 psi -- to provide enough fuel for the fuel-to-air ratio needed to run the engine.