Electric Fuel Pumps – Design, Work and Faults
Electric fuel pump is used in modern internal combustion engines to supply fuel from the fuel tank to the injectors. The pump should deliver fuel under high pressure, so that the nozzle can spray it into the engine. For the proper engine operation fuel pressure should be within allowed specifications for a given engine. Too low-pressure can lead to “fuel starvation” engine misfire, excessive vibration or stop the engine under load. Too much pressure causes uneven engine running too rich mixture, and excessive pollution.
Electric fuel pumps are usually installed in fuel tank (intake), although some can be installed outside. Some cars may be equipped with two pumps (one pump inside the tank and the main pump on the outside). The location of the pump in the fuel tank helps mute the buzzing noise of pump’s electric motor. Submersion into the fuel helps lubricate and cool the pump’s engine. Driving with fuel tank filled with less than ¼ of its volume can shorten the life of the pump and cause rapid overheating. It also increases risk of pump left without of gas during rapid acceleration or deceleration.
The pump is usually part of a module that also includes a float that carries electrical signals to the level indicator, located on the dashboard. If the fuel pump needs replacing, it can be replaced separately or the complete module assembly (it is expensive, but much easier).
Different electric fuel pumps have different designs. Some older designs used to use forced displacement of the circulation pump chamber. This type of pump can produce very high pressure and constant flow. But at the outlet of the fuel pump has been strong pressure fluctuations, so often in the gas line after the pump was installed damper to reduce the amplitude of pulsation of gas pressure. Circulating chamber can also be installed outside the tank and used with the second low-pressure pump installed in the fuel tank.
There is another type of fuel pump – “rotor-type”. This design is similar to design of the oil pump and uses the offset rotor to push the fuel through the pump. Another variation of the roller pump – “vane-type”. The blades are used instead of rollers to push the gas through the pump. Most modern cars use a pump turbine. Blades of the impeller push gas through the pump. Turbine type pumps do not produce the pressure fluctuations these types are less complicated to manufacture and more reliable in operation. It is possible to replace a fuel pump by not original unit. In this case fuel pump’s output should be within original specifications and as consumption the same as the original one. Use of an improper specs can cause deterioration of performance of the car.
How does electric fuel pump work?
When the ignition, the electronic control unit excites the relay, which supplies voltage to fuel pump, its motor starts to rotate, and within a few seconds it creates necessary gas pressure. Fuel feeds into the inlet pump through a mesh filter to delay the rust and dirt. Outlet of the pump the gas passes through the check valve, single acting (valve maintains a residual pressure in the system, when pump does not work) and feeds to the engine through the fuel line and filter. The fuel filter catches any rust, dirt and other solid contaminants that have passed through the pump to prevent the penetration of these particles in the injectors.
Further, the gas enters the fuel rail, located on the engine and from the rail to each injector. Fuel pressure regulator, located on the ramp, maintains the fuel pressure and throws any excess back to the tank. Start the engine and the electric fuel pump starts to operate continuously and to keep pumping gas until the engine is running. If the engine stops, then the electronic control unit receives a signal from the sensor and the crankshaft ECU will turn off the pump.
A lot of cars (especially Fords) have an inertial emergency switch which disables the fuel pump in the event of an accident. It is envisaged to reduce the risk of fire when the fuel line is damaged. To return the emergency transmitter to its original state – press the reset button on the sensor. On older cars pumps operated at a constant speed. In newer designs pump’s speed is being controlled by the electronic control unit in order to precisely match allowed specifications.
Fuel pump failure
The fuel pump can fail for several reasons: – Due to the presence of contaminants inside the fuel tank (dirt or rust); – When driving out of gas; – As a result of overheating (in constant motion with a low level of gas in tank); – Low voltage (problems with electrical wiring); – As a result of overloading (for a clogged fuel filter excessive resistance of the filter element can cause an overload of electric motor pump). The harder the conditions of the fuel pump, the more power is required for its operation. Electric fuel pump often fails without any warning. You may drive your car without a trouble, and within a minute the pump fails, the engine just stalls and the car gets up in the middle of the road. Or in the morning you are going to start the car but the engine just will not start.
By what signs can one predict the damage the fuel pump? One way is to listen to the noise of the pump when the ignition is on. Complete absence of noise indicates that it is not working. It can be caused by a malfunction of the pump, pump relay malfunction, the fuse or the lack of voltage. On most cars when fuel pump fails you wouldn’t see usual Check Engine light on. Most modern engines equipped with the union to check the fuel pressure on the ramp nozzles. Connecting fuel pressure gauge to the fitting check valve will quickly show whether the pump produces pressure or not. On engines without pressure test union, to measure pressure can be done by connecting directly to the fuel line at the junction of the ramp. If the gauge indicates zero – the pump does not work. If the pressure is less than nominal, it will be necessary to carry out further diagnosis to identify the causes of low fuel pressure. Fire Fighting Hose Nozzles