Fuel Injector

Battery voltage for injectors is supplied from main relay and then passes through injector resistor before reaching injectors. Injectors are energized when ECU supplies a ground circuit for individual injectors. When solenoid coil is energized, plunger valve lifts off plunger seat and pressurized fuel is injected at intake valve. Because plunger valve lift and fuel pressure are constant, air/fuel ratio is determined solely by length of time that injector is open. Injectors are sealed by "O" rings or seal rings at top and bottom. These seals reduce operating noise, prevent air and fuel leaks and help insulate injector from radiated engine heat. See Fig 1 .

At start-up, air/fuel ratio must be enrichened. When ECU receives signals from starter switch indicating vehicle is cranking, ECU calculates injector duration from start-up calibration tables based upon engine speed and coolant temperature. This provides extra fuel needed for start-up.

During certain deceleration modes (throttle valve closed and engine speed greater than specification) and acceleration modes (engine speed greater than specification), ECU will activate its fuel cut-off control function by de-energizing injectors. This improves fuel economy and prevents engine from over-revving.

Fig 1: Typical Fuel Injector Assembly