An electric fuel pump, filter and an electronic device makes up a fuel assembly. The function of the electronic device is to sense the volume of the fuel in the tank. An electric fuel pump’s function is to pump fuel from the gas tank to the injectors. The pump has to maintain a high pressure of 30 to 85 psi as per the application. This high pressure has to be maintained so that injectors can easily spray the fuel into the engine. The pump is powered by a motor which runs to maintain the pressure in the fuel system. Once the engine starts, the power-train control module (PCM) controls the motor in the pump through a timer and a relay. Thus PCM has full control over the pump by deciding the duration for which the pump will run. There is an inlet tube through which the fuel enters the pump. The impurities like rust and dirt are filtered out of the pump by a mesh filter. At the outlet of the pump there is a one way check valve which allows easy exit of the fuel from the fuel pump. Fuel enters fuel supply rail which is fitted with fuel pressure regulator. This pressure regulator maintains the necessary volume of the fuel to injectors and any excess fuel is transmitted back to the tank.
There are two types of Electric fuel pumps: Electric In-Tank Fuel Pumps and Electric External Fuel Pumps. Electric In-Tank Fuel Pumps are more common than the Electric External Fuel Pumps.
Electric In-Tank Fuel Pumps
This pump is mounted in the fuel tank of the vehicle itself. The operating pressure varies from 9-55 psi. The fuel flow in the injection system can go up to 45 gallons per hour. The In-tank fuel pump is accessed from the top by making a hole under the rear passenger seat. These pumps are designed such that they function always in immersed condition. The in-tank location helps in covering up the noise coming out of the fuel pump motor. There is one more advantage of having In-tank location. The motor is always immersed in the fuel which in-turn provides the necessary lubrication to the motor. This location also helps the motor in cooling down as well. Sometimes if you run out of the fuel, there is nothing which can provide necessary cooling and lubrication. Such condition can harm the fuel pump irreversibly.
Swirl Pot In-Tank Fuel Pumps are placed on swirl pots. Swirl pot allows for a continuous delivery of the fuel by keeping air away from the fuel system. If air gets into the fuel system it interrupts the continuous flow of fuel in the fuel system. If swirl pot is correctly installed it reduces the injection pump failure. It smoothly filters the fuel from fuel tank.
Electric External Fuel Pumps
External electric fuel pump is powered by electric power and is housed outside the fuel tank securely on a body panel. The pumps make use of a siphon to extract fuel from the fuel pump. Siphon is a tube used to draw fuel upwards from a tank or reservoir making use of gravity. After that they push the fuel up towards the engine. The pumping action of the fuel pump is controlled via a relay. Fuel pump failures are often reported when fuel level runs low and debris and other solid particles are transferred to the pump. External fuel pumps make use of rubber bushings to ward off dangers from road shocks. Since the fuel pump is located outside the fuel tank and not immersed in the fuel, the additional arrangements for lubricating and cooling the motor has to be made.