Fuel Pump: Description and Operation

Fuel Pump Cut-away:

The electric fuel pump (roller cell type) which is located in the fuel tank, supply fuel to the injection valves. Operation of the pump is controlled by the fuel pump relay which is energized by the Motronic control unit. The relay will only be energized during cranking (starting) or while the engine is running. The DME control unit uses the engine speed signal as an input for fuel pump control.

Since the fuel pump is located within the fuel tank the electric motor is well cooled, while also avoiding problems with lubrication and seal seepage. There is no danger of explosion because there is never an ignitable mixture in the common housing for pump and motor. In order to maintain the pressure in the fuel system under all possible operating conditions, the pump supplies substantially more fuel than the internal combustion engine needs at maximum engine loads.

Fuel Pump View:

The roller-cell pump itself consists of a cylindrical hollow chamber in which an eccentrically fitted rotor disc rotates. This is fitted with metal rollers which are held in pocket-shaped recesses around the circumference. When the rotor disc rotates the rollers are pressed outwards by centrifugal force and act as a circulating seal. A pumping operation is effected by the circulating roller seals which draw in fuel at the inlet port and forces fuel through the outlet port against the pressure regulator valve on the injector rail.