Fuel Pressure Regulator

The fuel pressure regulator is a sealed unit, divided into 2 chambers (fuel and spring) by a diaphragm. The fuel chamber receives fuel through the inlet side of the fuel injector rail. The spring chamber is connected to intake manifold vacuum.

At idle, intake manifold vacuum is high. The diaphragm is pulled back by intake manifold vacuum, and excess fuel is returned to the fuel tank. As throttle opens, intake manifold vacuum decreases. The regulator spring overcomes manifold vacuum, increasing fuel pressure.