Fuel Pressure Regulator: Description and Operation

Pressure Regulator And Vacuum Hose:

LOCATION

The regulator is mounted on the output end of the fuel rail and is connected to intake manifold vacuum. The fuel return tube is connected to the fuel pressure regulator.

PURPOSE

The regulator is calibrated to maintain fuel system pressure at approximately 214 kPa (31 psi). This is with vacuum applied while the engine is at idle. Fuel pressure will be 55-69 kPa (8-10 psi) higher if vacuum is not applied to the regulator.

OPERATION

Fuel Pressure Regulator Operation (Typical):

The fuel pressure regulator used is a vacuum balanced, nonadjustable type. The pressure regulator contains a diaphragm, calibrated spring and a fuel return valve. Fuel pressure operates on one side of the regulator, while spring pressure and intake manifold vacuum operate on the other side. Spring pressure on one side of the diaphragm tries to force the return valve closed. Fuel pressure on other side of diaphragm, with assistance from manifold vacuum on spring side of diaphragm, act against spring pressure to open return valve. System fuel pressure is the amount of fuel pressure required to force against spring pressure and unseat return valve.

Without vacuum applied to the spring side of the regulator, the spring is calibrated to open the fuel return outlet. This happens when the pressure differential between the fuel injectors and the intake manifold reaches approximately 269 kPa (39 psi). Since manifold vacuum varies with engine operating conditions, the amount of vacuum applied to the spring side of the diaphragm varies. For this reason, fuel pressure varies, depending upon intake manifold vacuum. With low vacuum, such as during wide open throttle conditions, minimal vacuum assistance is available. Full spring pressure is exerted to seal the fuel outlet. This causes the system pressure to increase. With high vacuum, such as during idle, fuel pressure on one side of the diaphragm is balanced by intake manifold pressure. This is done on the spring side of the diaphragm and results in lower system fuel pressure.