Main Pump

Fuel Tank And Pumps:

PURPOSE AND LOCATION
The main fuel pump delivers pressurized fuel to the injector rail to provide the injectors with a constant fuel supply. It is located under the left side of the chassis, ahead of the rear wheels.

The fuel pump operates during engine cranking and when the engine is running. If the engine stops while the ignition is on, the injection ECU shuts off power to the fuel pump to reduce the risk of fire in the event of an accident.

Fuel Pump (Typical):

CONSTRUCTION
The main pump is a centrifugal roller-type pump consisting of a pump chamber, electric motor, pressure limiter, and check valve. The electric motor actually operates in the fuel in the fuel pump housing. This is possible, because the housing never contains an ignitable mixture. The fuel is used as a lubricant and coolant for the pump motor.
A check valve is incorporated in the fuel outlet and a pressure limiter valve is located on the pressure side of the fuel pump housing with a return passage to the fuel inlet side.

Roller Pump (Located In Fuel Pump):

The pump chamber is a cylinder in which an eccentrically fitted pump rotor disc rotates. This is fitted with metal rollers which are held in pocket-shaped recesses around the circumference.
In order to maintain a constant pressure in the fuel system under all possible operating conditions, the pump supplies substantially more fuel than the engine would ever need at any engine load.

OPERATION
When the rotor disc rotates, the rollers are pressed outwards by centrifugal force and act as a circulating seal. A pumping action is created by the circulating rollers which draw in fuel at the inlet port and force the fuel through the discharge port into the fuel system.
When the pump is shut off, the check valve in the fuel outlet will close, prohibiting fuel from returning to the fuel tank via the fuel pump. The check valve maintains a pressure in the fuel lines called "rest pressure".

The maximum fuel pump pressure (not fuel system pressure) is dependent on the calibration of the pressure limiter. If the fuel pump pressure exceeds a preset limit (for example a clogged fuel filter), the pressure limiter will open a by-pass to the fuel inlet side of the pump.