Fuel Injector: Description and Operation

Fuel Injector - Cutaway View:

The fuel injectors are solenoid operated valves that deliver fuel, in a metered amount, to the combustion chambers of individual cylinders. When the solenoid coil is energized, the plunger is retracted lifting the needle valve off its seat, allowing fuel to be injected into the combustion chamber. When the solenoid is de-energized spring pressure closes the valve.

Since the injection nozzle opening is a fixed size and the fuel pressure is also fixed (55 psi), the amount of fuel that is injected is determined by the amount of time that the needle valve remains open. This time is commonly referred to as the "pulse width" of the injector. The SBEC controls the pulse width of the injector to change the air/fuel ratio for varying engine driveability conditions.