Fuel Pressure Regulator
The pressure regulator (2 regulators on Porsche 928) consists of a sealed, spring loaded diaphragm with a connection for intake manifold vacuum. Fuel is provided to fuel injectors under approximately 36 psi (2.5 kg/cm2 ) pressure.
A connection for intake manifold vacuum provides a constant pressure differential which ensures that the amount of fuel injected is solely dependent upon injector "open" time. Excess fuel is returned to fuel tank. No service of pressure regulator is required.