Electric Fuel Pump

What is Electric Fuel Pump
An electric fuel pump is used on engines with fuel injection to pump fuel from the gas tank to the injectors.
The pump must deliver the fuel under high pressure (typically 30 to 85 psi depending on the application) so the injectors can spray the fuel into the engine. 
Fuel pressure must be within specifications for the engine to run correctly. 
Too little pressure can starve the engine for fuel, causing it to run lean, misfire, hesitate or stall. 
Too much fuel pressure can cause the engine to run rough, waste fuel and pollute.

How an Electric Fuel Pump Works
  • When the driver turns the ignition key on, the Powertrain Control Module (PCM) energizes a relay that supplies voltage to the fuel pump. 
  • The motor inside the pump starts to spin and runs for a few seconds to build pressure in the fuel system. 
  • A timer in the PCM limits how long the pump should run until the engine starts. 
  • Fuel is drawn into the pump through an inlet tube and mesh filter sock (which helps keep rust and dirt out of the pump). 
  • The fuel then exits the pump through a one-way check valve (which maintains residual pressure in the system when the pump is not running), and is pushed toward into the engine through the fuel line and filter. 
  • The fuel filter traps any rust, dirt or other solid contaminants that may have passed through the pump to prevent such particles from clogging the fuel injectors.
  • The fuel then flows to the fuel supply rail on the engine and is routed to the individual fuel injectors. 
  • A fuel pressure regulator on the fuel rail maintains fuel pressure, and routes excess fuel back to the tank.

  • On newer vehicles with returnless EFI systems, the fuel pressure regulator is located in the fuel tank and is part of the fuel pump module. There is no fuel return line from the engine back to the tank.
  • The fuel pump runs continuously once the engine starts, and continues to run as long as the engine is running and the ignition key is on. 
  • The pump may run at a constant speed, or it may operate at a variable speed depending on engine load and speed. 
  • If the engine stalls, the PCM will detect the loss of the RPM signal and turn the pump off.
  • Many vehicles (Fords, notably) also have an "inertia safety switch" that shuts off the fuel pump in the event of an accident. 
  • This is done to reduce the risk of fire should a fuel line be ruptured. A hard jolt trips the safety switch and opens the fuel pump circuit. This required manually resetting the safety switch after the incident by pressing the reset button on the switch.
  • On most older vehicles, the fuel pump runs at a constant speed. But on many newer applications, the pump speed is varied by the PCM to more closely match the engine's fuel requirements

Some more details about Electric Fuel Pump
  1. Electric fuel pumps are usually mounted inside or sometimes outside the tank. 
  2. Some vehicles may even have two fuel pumps (a transfer pump inside the tank, and a main fuel pump outside). 
  3. The in-tank location helps in reducing the buzzing noise produced by the electric pump motor, and immersing the pump in fuel helps lubricate and cool the pump motor. 
  4. Minimum a 250ml of fuel is required in the pump., or else the pump gets over heat and may damage. 
  5. The pump is usually part of the sending unit assembly, that includes a float that sends an electrical signal to the fuel gauge on the instrument panel. 
  6. Electric fuel pumps come in a variety of designs. Some older applications use a positive displacement "roller cell" pump. This type uses rollers mounted on an offset disc that rotates inside a steel ring. Fuel is drawn into the spaces (cells) between the rollers and pushed along from the pump inlet to the outlet. Roller cell pumps typically spin about 3,000 rpm. This type of pump can generate very high pressure, and the flow rate tends to be constant. But the output comes in pulses, so a muffler is often mounted in the fuel line after the pump to dampen pressure pulses. 
  7. A roller cell pump may also be mounted outside the fuel tank, and used with a second low pressure supply pump mounted inside the fuel tank.
  8. Another type of positive-displacement pump is the "gerotor" pump. This design is similar to that of an oil pump, and uses an offset rotor to push fuel through the pump. A gerotor pump typically operates at around 4,000 rpm.
  9. Another variation is the roller vane pump. Here, vanes are used instead of rollers to push fuel through the pump.
  10. Most newer vehicles use a "turbine" style fuel pump. A turbine pump has an impeller ring attached to the motor. The blades in the impeller push the fuel through the pump as the impeller spins. This type of pump is not a positive-displacement pump, so it produces no pulsations, runs very smoothly and quietly. It operates at higher speeds, typically up to 7,000 rpm and draws less current than older style pumps. It is also less complicated to manufacture and is very durable. Some aftermarket pump supplies use this type of pump to replace the older designs.

#Automobile Engineering, injection system, fuel pump