Cherokee 2WD L4-150 2.5L VIN H TBI (1988)
Fuel Pressure Regulator: Description and Operation
Fuel Pressure Regulator
The fuel pressure regulator is an overflow type attached to the throttle body. The regulator is adjustable and controls the amount of fuel system pressure
available to the fuel injector. Fuel pump output pressure is above that needed to operate the fuel system, and excess fuel is returned to the fuel tank
through the regulator via the fuel return line. The regulator consists of a spring chamber, a calibrated spring, a diaphragm, and an adjusting screw. A
lead plug seals the adjusting screw hole. When fuel under pressure enters the top of the regulator, the relief valve and spring are forced down, opening a
passage to the fuel return line. A pivot on top of the diaphragm keeps the diaphragm from tipping . The amount of pressure required to force the
regulator spring down determines the fuel system operating pressure. The adjustment screw allows that pressure to be set. Turning the screw in will
increase the fuel pressure, and turning it out will decrease the fuel pressure. A small vent passage in the throttle body, vents the spring chamber to
atmosphere, and the injector tip is also vented to atmosphere. Due to this venting process fuel system pressure bleeds rapidly to zero when the engine is
not running.
