- Do It Yourself Auto Repair
The Fuel Pump : Workhorse of the Car Fuel System
The automotive fuel pump is a critical part of the car fuel system, delivering pressurized fuel from the fuel tank, through the lines of the fuel system, to the fuel injectors, and ultimately to the inside of the engine where it is burned to drive the vehicle. In modern automobiles, the fuel pump is often called the fuel pump module, and includes the motorized fuel pump, as well as any electronic controls that turn the pump on and off. The sending unit for the gasoline gauge, or fuel gauge is also often located within the fuel pump module. The fuel pump module also includes a pick-up tube for drawing gasoline in from the tank, and possibly a pick-up screen or filter as well.
Operation of the Car Fuel System
When the ignition is turned on in most vehicles, the power train control module turns on the power to the fuel pump module for around two seconds to pressurize the car fuel system in anticipation of vehicle start up. If the vehicle is not started, the fuel pump module is turned off, to be reactivated if the operator turns the ignition key to the start position. The pressurized fuel is delivered through the fuel lines to the fuel injectors, which control the flow of fuel into the engine using electronics and mechanical valves. Some vehicles use a return fuel line to deliver excess fuel back to the fuel pump module.
Car Fuel System Diagram
Fuel Pump Failure
Fuel pump module failure is often sudden, and you will probably first notice it when you attempt to start the vehicle, and it fails to start. In some cases, the pump module may fail to operate when you are driving down the road, causing the engine to suddenly stall. Failure may either be internal to the pump motor, or can be in the wiring that delivers the power to the fuel pump module from the power train control module. Sometimes, the failure may be in another part of the vehicle electrical system causing a secondary fuel pump failure. Another sign of failure in some vehicles is when the fuel gauge fails to operate correctly. Fuel pump failure should be diagnosed and confirmed by a professional automotive technician before a pump is replaced, since other vehicle problems can mimic a fuel pump failure.
What's Inside of a Car Fuel Pump?
The fuel pump module in most modern vehicles is located inside of the fuel tank, and is accessed for service through the top of the tank. In many vehicles, this requires complete removal of the fuel tank, although some vehicles have access points under the rear seat or trunk floor to allow for easier replacement of the fuel pump module. Fuel tank module replacement can be particularly difficult if the fuel tank is full of fuel. If your car fails to start, and you suspect a fuel module problem, you may be able to start the vehicle by pounding on the bottom of the fuel tank firmly with a rubber hammer. The vibration may jar the motor inside of the module loose, and allow the pump to start turning and functioning. This is a temporary repair, and may allow you to drive the vehicle to a service facility, but you should plan for replacement of the module as soon as you can. If your vehicle has a fuel filter, service it regularly to present clogging, which can interrupt the fuel flow, or make the car fuel pump work harder than necessary, causing early failure.