Fuel Pressure Regulator

Fuel Pressure Regulator, Vacuum Hose Removed:

The fuel pressure regulator is mounted on the fuel rail. The primary function of the regulator is to maintain a constant pressure difference between the fuel pressure at the injector nozzles and the absolute air pressure (manifold vacuum) in the intake manifold. This is because the ECU meters fuel by modifying only the "ON" time of the injector. The ECU, during its fuel metering calculations, relies on the pressure differential remaining constant. To accomplish this goal the regulator has a vacuum line to sense intake manifold pressure. With this input the regulator can control the fuel pressure, in direct response to intake manifold pressure (vacuum) fluctuations.

Fuel Pressure Regulator (Cut-Away View):

Control vacuum is applied to a diaphragm which operates a pressure valve. When the engine is under very light load, the control vacuum is high, spring pressure against the regulator valve is reduced and the fuel system is regulated at a lower pressure. When the engine is under heavy load (as in wide open throttle operation), manifold absolute pressure increases and the control vacuum is low. More spring pressure is applied to the valve and fuel system pressure is increased by the same amount as the manifold absolute pressure, to maintain a constant differential.