Fuel Pump: Description and Operation

FUEL PUMP CONTROL




- The ECM receives a signal emitted from the crankshaft position sensor and turns the fuel pump relay ON or OFF to control fuel pump operation. To improve safety, the fuel pump will stop if the engine stalls with the ignition switch ON.


PURPOSE/OPERATION
The impeller type fuel pump consists of a motor, impeller, pump casing, pump cover, relief valve, check valve and pump filter. It is built into the fuel tank together with the fuel meter unit to provide quiet operation.





1. When the engine starts, fuel pump relay activates. this operates the motor to rotate the impeller.
2. Fuel entering a vane groove of the impeller flows along the fuel passage and into the next vane groove by centrifugal force. during the time fuel flows from one groove to the next, a pressure differential is produced by friction of the flow.
3. Thus, fuel pressure increases while the action is described in step 2. above is repeated, and fuel is discharged from the pump casing. Fuel under pressure then passes through the clearance between the armature and the magnet and is discharged from the fuel pump.
4. As fuel discharge pressure reaches the specified value, the relief valve opens. This discharges fuel under pressure into the fuel tank. Fuel from the fuel tank then returns to the suction port and passes through the fuel pump. This action of fuel flow is repeated. In this manner, the relief valve prevents an abnormal increase in fuel pressure.
5. When the engine and fuel pump stop, spring force acts on the check valve to close the discharge port so that fuel pressure remains in the fuel delivery line.