W 150 Pickup V6-239 3.9L (1991)
Fuel Pressure Regulator: Description and Operation
Fuel Pressure Regulator
The fuel pressure regulator is mounted to the rear of the throttle body. The regulator's primary purpose is to keep the fuel pressure at 14.5 psi. When the
fuel pump is operating, fuel flows past the injectors and into the fuel pressure regulator. The fuel return port is blocked by a spring loaded rubber
diaphragm. When the fuel pressure reaches 14.5 psi, the rubber diaphragm moves away from the fuel return port, allowing fuel to return to the tank.
The rubber diaphragm is constantly covering and uncovering the fuel return port to maintain the specified 14.5 psi.
The pressure regulator is also controlled by manifold vacuum. At idle or deceleration, when manifold vacuum is at its highest level, vacuum assists in
lifting the rubber diaphragm uncovering the fuel return port. When the vehicle is in wide open throttle, vacuum is at its lowest level, the pressure
regulators spring will push the rubber diaphragm over the fuel return port to increase the fuel pressure.
