Fuel Pressure Regulator: Description and Operation

Fuel Pressure Regulator
The fuel pressure regulator (Fig 1) is attached to the main fuel rail and consists of a metal housing containing a spring loaded diaphragm. When the pressure setting of the regulator is exceeded, the diaphragm moves, exposing an opening to an overflow duct which allows excess fuel to return to the fuel tank, causing a drop in fuel pressure. The reduced fuel pressure allows the diaphragm to move back to its original position, thereby closing the fuel return outlet. This sequence of events is repeated as long as the pump is running. In this way, fuel pressure is held constant as fuel demand varies. The pressure setting is adjusted to the correct value during production when the outer spring housing is compressed until the correct spring load is obtained. This is not adjustable in service.

The spring housing of the regulator is sealed and connected to the engine inlet manifold by a small bore pipe. By allowing it to sense inlet manifold depression, the pressure drop across the injector nozzle remains constant because the fuel pressure will alter as manifold depression alters. This arrangement ensures that the amount of fuel injected is only dependent on the the duration of injector open time.

System fuel pressure is 3 bar (43.5 lb/in2) above manifold pressure.

The three way vacuum valve is fitted to the fuel rail to prevent weak fuelling after a hot start.