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The fuel injectors are solenoid operated valves that are normally closed.When a fuel injector solenoid is energized (pulsed) the injector needle valvemoves, allowing pressurized fuel to pass through the injector and mix withthe air entering the engine. Each fuel injector (there is one for each enginecylinder) is mounted in the intake manifold and is positioned to spray fuelinto a cylinder head intake port.

The Engine Control Module (ECM) controls injector timing and pulse width(how long the fuel injectors are turned on). The ECM pulses the fuel injectorsbased on information provided by its network of engine sensors. The ECM usesthe crankshaft position sensor to determine when to pulse the injectors. Enginecoolant temperature, intake air temperature, air flow and throttle positiondata are all used by the ECM to calculate injector pulse width.

The ECM also uses its network of sensors to determine whether all injectorsshould be pulsed at the same time (simultaneous injection) or each injectorshould be pulsed individually (sequential injection). Sequential injectionis almost always used during normal engine operation and simultaneous injectionmay be used when the engine is being cranked.