Fuel Pressure Regulator: Description and Operation

Throttle Chamber:

PURPOSE
Maintains fuel pressure at 21 psi (147 kPa) above manifold pressure.

OPERATION
Fuel flows from the pump, through the lines, to the throttle chamber and injector, to the pressure regulator. Fuel pressure acting on the diaphragm opens the return line orifice to the fuel tank. As manifold vacuums lowers (during accel), the spring in the diaphragm closes the passage, increasing fuel pressure.
As manifold vacuum increases, the spring tension is overcome and the orifice is opened, allowing more fuel to return to the tank, lowering fuel pressure.