Fuel Pump: Description and Operation

Fuel Pump
The fuel pump (Fig 3) has a roller type cell driven by a permanent magnet electric motor. A small rotor is mounted on a armature shaft and rotates in an eccentric housing.

The rotor contains five metal rollers each one housed in a cutaway on the circumference of the rotor. When the armature rotates centrifugal force acting on the rollers forces them against the metal housing forming a seal. The trapped fuel is then forced to the pressure side of the system.

The pump is designed as a so called 'wet pump' which means the motor is full of fuel. However, the motor never contains an ignitable mixture, even when the tank empties.

The pump is controlled by the ECU via a relay and is energized for a short period when the ignition is switched on in order to pressurize the fuel rail. The pump will not operate again until a signal is received by the ECU from the starter relay or when the engine is running and the ECU receives speed signals from the ignition HT coil.

For safety an inertia switch is fitted to switch off the entire fuel system.