Fuel and Air Intake
A mechanical fuel pump is most often used on cars with carburetors. This type of pump produces low pressure and is usually driven by the engine. Cars all use electric fuel pumps nowadays because of the universal application of fuel injection and its need for higher pressures. Electric fuel pumps are almost always located inside the gas tank, but there are some applications where the pump may be located along the frame or uni-body channel. The pump has a strainer at its pickup to filter out contaminants and uses an electric motor for power. Fuel is used as a lubricant and coolant for the motor. The electric fuel pump has its own electrical control circuit, typically consisting of wiring, a fuse and a relay. This circuit interacts with the car's powertrain control module (PCM), which governs and monitors fuel pump operation.
The fuel pump provides fuel with the proper pressure and volume for delivery by the carburetor or fuel injection system. The electric fuel pump circuit also employs various safeties that stop the pump from running in the event of an accident.
Mechanical fuel pumps require no maintenance, but should be replaced at the first sign of a problem. Pressure or volume may drop off, giving an early warning sign of impending pump failure. A professional service technician can usually identify a pump problem quickly. With fuel-injected vehicles, regular fuel filter changes can help extend the life of the electric fuel pump. It's best to replace the filter every two years or 40,000 kilometres. A contaminated filter can restrict fuel flow from the electric fuel pump, eventually taking a toll on its life. You can also help protect the pump by keeping the tank at least half-full at all times. Since fuel cools the pump, having plenty of fuel in the tank helps keep the pump from getting too warm, which could damage it. Another good reason to keep the gas tank at least half-full is to reduce the chances of sediment pick-up at the fuel pump inlet strainer. A restricted strainer can starve the pump, causing it to overheat and fail. If you own a Ford or Lincoln-Mercury vehicle, check your owner's manual for the location of the fuel pump shut-off switch. This switch is designed to electrically disconnect the fuel pump in the event of an accident. Sometimes, an abrupt jarring of your car may be enough to cause this switch to open. It's good to know where the switch is so you can try resetting it if your car does not start. A faulty electric fuel pump can cause various symptoms including a loud pump whine, engine no-start, hesitation, poor performance and stalling. If your car demonstrates any of these performance problems, have it checked out by a qualified service technician. Replacing the fuel pump generally involves removal of the fuel tank.