Fuel pressure regulator

Fuel pressure regulator

The fuel pressure regulator is a mechanical device mounted to the fuel rail. Its purpose is to control the fuel rail pressure with respect to the inlet manifold depression. The fuel rail pressure must be reduced at high manifold depressions to avoid excess fuel being drawn through the injector nozzles.

The fuel regulator contains a spring loaded diaphragm valve with pressurised fuel on one side of the diaphragm and manifold vacuum acting on the other. When fuel rail pressure, assisted by manifold depression, overcomes the diaphragm spring load , fuel flows past the diaphragm valve to the fuel tank, reducing fuel rail pressure. With manifold depression low, during hard acceleration, the fuel rail pressure must be high to overcome the diaphragm spring load. With manifold depression low, during coast down, the vacuum acting on the diaphragm valve acts against the spring load and a lower fuel rail pressure lifts the valve from its seat.

Idle air control valve (IACV)

Engine idle speed is maintained by the IACV, connected to the stepper motor and controlled by the ECM. With the throttle butterfly fully closed, a small quantity of air is able to by-pass the throttle butterfly via the base idle passage. The ECM monitors engine speed and load via sensors around the engine. Should extra air be required to maintain a steady idle speed, the ECM signals the stepper motor to operate a number of steps and open the IACV to allow air through the throttle by-pass. The stepper motor operates over a range of 180 steps with the IACV fully open at 0 steps and fully closed at 180 steps.