Fuel Injector: Description and Operation

Typical Fuel Injector Construction:

The Fuel Injectors, located at the intake ports on the engine, are electrical solenoid valves. They open by an electric signal from the ECU and close by spring pressure when the signal is removed. When current is sent through the coil windings, electromagnetic force lifts the solenoid, (which is connected to the needle valve), and fuel is expelled. The lift is about 0.006 in. and lasts about 0.001 second. The pintle on the tip of the injector helps to atomize and distribute the fuel discharge.

Because the amount of lift is always constant, the only way volume can be varied is by the time the injector remains open. This is called pulse width or duration. Various factors determine pulse width based on input from several engine sensors and control processing by the ECU. Refer to COMPUTERIZED ENGINE CONTROLS for information concerning these sensors and the ECU. The injectors are electrically "hot" all the time and the ECU completes the ground circuit. Actual injector pulse operation takes place twice per four stroke cycle, in other words, once per crankshaft revolution.