Comanche 4WD L4-150 2.5L VIN P MFI (1991)
Fuel Pressure Regulator: Description and Operation
Fuel Pressure Regulator
The fuel pressure regulator is mounted to the output end of the fuel rail, and is a vacuum assisted non-adjustable type. The vacuum source comes from
the intake manifold, and the regulator is calibrated to maintain fuel system pressure at about 214 kPa (31 psi) with vacuum applied and the engine at idle.
With vacuum disconnected the fuel pressure will be about 55-69 kPa (8-10 psi) higher. The regulator contains a calibrated spring, a diaphragm, and a
fuel return valve. Fuel system pressure provided by the fuel pump exists on one side of the regulator, while spring pressure and manifold vacuum are
present on the other side. Spring pressure on one side of the diaphragm forces the fuel return valve closed, and fuel pressure, with vacuum assistance
forces the return valve open. Fuel system pressure is the amount of fuel pressure with vacuum assistance required to open the fuel return valve, against
spring pressure. By using vacuum assistance it is possible to vary the fuel system pressure based upon varying engine conditions, such as wide open
throttle, low vacuum, which will cause an increase in fuel pressure at the time it is most needed. At high vacuum conditions, such as idle and
deceleration, fuel system pressure will decrease, when there is no need for extra fuel.
