Vanden Plas L6-4.0L (1990)
Fuel Pressure Regulator: Description and Operation
Fuel is pumped to the fuel rail and injectors, where fuel pressure is controlled by the fuel pressure regulator. Excess fuel, above the engine
requirement, is returned to the fuel tank. The pressure regulator spring chamber above the diaphragm is referenced to intake manifold vacuum. The
differential pressure across the fuel injector nozzles is therefore maintained constant at 3.0 bar (44 psi) and the quantity of fuel injected for a given
injector pulse duration is also constant. Fuel pressure measured on a test gauge will vary between 2.3 bar (32 psi) at overrun to 3.0 bar (44 psi) at
full load.
The fuel pressure regulator is located as close as possible to the fuel rail so that good dynamic control of fuel pressure is achieved. This design
provides the same pressure across each injector, and delivers an equal quantity of fuel to each of the six cylinders.
The main component of the pressure regulator is the diaphragm, below which a steel ball valve is mounted on a disc. The upper side of the
diaphragm incorporates a spring retaining cup. Spring length is set during manufacturing by deforming the top cover until the fuel pressure at
which the diaphragm lifts at atmospheric pressure is set at 3.0 bar (44 psi). A filter screen prevents any small pieces of debris from the fuel rail
becoming trapped under the disc.
The tube on the top of the upper case is connected to the intake manifold. During engine operation, intake manifold vacuum "assists" the
pressurized fuel to lift the diaphragm against the spring. When fuel pressure exceeds the control value, the valve lifts off the seat allowing a
portion of the fuel to be directed to the outlet port, thereby maintaining fuel pressure at the control value. The excess fuel is returned to the fuel
tank.
Fuel Pressure Regulator
