MPFI Injector

The injectors are supplied with 12 volts from the ignition/fuel relay. Drivers in the ECM supply a ground to the other terminal of the injector to actuatethe solenoid.

The ECM energizes the injector solenoid, which opens a ball valve allowing pressurized fuel to flow through a flow director plate that has a number (4-8) of machined holes creating a conical pattern of finely atomized fuel.

The fuel is directed at the intake valve aiding in valve coolingand additional atomization.

The multi-port system uses 2 injector drivers.

The amount of fuel injected is determined by the length of time that the injector is energized, called Pulse Width.

The unit of measure used for injector “on”time is milliseconds.

Again, as with the TBI injectors, the pulse width is based on the fact that an injector discharges a known amount of fuel per millisecond at a specific fuel pressure and at a specific supply voltage, so maintaining proper pressure is ESSENTIAL to providing proper air/fuel ratio.

When injectors stick or seize, no fault code will be set. Injector codes set for opens or shorts in the driver circuit back to the ECM.

The regulator is a diaphragm operated relief valve with fuel pressure on one side of the diaphragm and opposing spring pressure and manifold vacuum on the other.

The regulator’s function is to maintain a constant effective pressure at the injector tips at all times.

The addition of manifold vacuum is necessary because injector tips are located inside the manifold, this would normally cause the pressure drop at the tipto change with manifold vacuum. With manifold vacuum acting on the regulator diaphragm the effective pressure at the tip remains constant.

The regulator compensates for engine load by increasing fuel pressure as engine vacuum drops, this will cause the gauge to fluctuate with throttle opening while checking pressure. Fuel system pressure is checked with the engine off and the fuelpumps running or with the engine running and the vacuum hose to the regulator disconnected.