Fuel Injector
Fuel injector is mounted in throttle body so that fuel is injected into incoming airflow. When voltage is supplied to injector solenoid, armature and plunger move upward against spring. Check ball above injector nozzle moves off seat and opens small orifice at end of injector.
Fuel supplied to injector is forced around ball and through orifice, resulting in fine spray of fuel. Volume of fuel injected is dependent only on length of time that injector is energized by ECU as fuel pressure is constant at injector. During cold engine starts, extra fuel is supplied so richer mixture will aid in starting. See Fig 1.