Fuel Pressure Regulator: Description and Operation

Fuel Pressure Regulator:

PURPOSE
Maintains a constant pressure differential between fuel pressure and intake manifold absolute pressure. Regulator increases fuel system pressure as manifold absolute pressure increases, so that the percent change in injection duration equals the percent change in the quantity of fuel injected. When manifold pressure is low (high vacuum), more fuel will spray from the injectors than will at high manifold pressure (low vacuum) for the same injection duration and fuel pressure.

In conjunction with pressure regulator control solenoid, system raises fuel pressure to reduce fuel percolation during hot restart.

LOCATION
End of fuel rail.

OPERATION
Control vacuum is applied to a diaphragm which operates a pressure valve. When the engine is under light load, control vacuum is high, spring pressure against the regulator valve is reduced and the fuel system is regulated at a lower pressure. When the engine is under heavy load (as in wide open throttle operation), manifold absolute pressure increases reducing control vacuum. More spring pressure is applied to the valve and fuel system pressure is increased by the same amount as manifold absolute pressure, maintaining a constant differential under changing engine loads.

The pressure regulator control (PRC) solenoid is installed in the vacuum line to the fuel pressure regulator. During hot re-start, the PCM energizes the PRC solenoid valve, which blocks manifold vacuum to the pressure regulator and vents the regulator diaphragm chamber to the atmosphere. With atmospheric pressure at the diaphragm, fuel pressure is increased. Increasing fuel pressure helps reduce fuel percolation due to heat. The PRC solenoid is energized for about 120 seconds after the engine is started. After this time, the PRC solenoid is turned "OFF" and normal vacuum modulation of fuel pressure is resumed.