The fuel pressure regulator is a diaphragm operated relief valve with injector pressure on one side and manifold pressure on the other. The function of the regulator is to maintain a constant pressure at the injector at all times.
The fuel pressure regulator is comprised of a pressure chamber, separated by a diaphragm relief valve assembly with a calibrated spring in the vacuum chamber side. The fuel pressure is regulated when the pump pressure acting on the bottom spring of the diaphragm overcomes the force of the spring action on the top side.
The diaphragm relief valve moves, opening or closing an orifice in the fuel chamber to control the amount of fuel returned to the fuel tank. Vacuum acting on the top side of the diaphragm along with spring pressure controls the fuel pressure. A decrease in vacuum creates an increase in the fuel pressure. An increase in vacuum creates a decrease in fuel pressure.
An example of this is under heavy load conditions the engine requires more fuel flow. The vacuum decreases under a heavy load condition because of the throttle opening. A decrease in the vacuum allows more fuel pressure to the top side of the pressure relief valve, thus increasing the fuel pressure.
The pressure regulator is mounted on the fuel rail and serviced separately. If the pressure is too low, poor performance could result. If the pressure is too high, excessive odor and a Code 45 may result.