Fuel Injector: Description and Operation

MPI Intake Manifold And Fuel Rail Assembly:

Fuel Injector:

The fuel injectors for the MPI system are electrically operated. The injectors get power whenever the fuel pump relay is turned on, and are energized individually when the ECU completes that circuit to ground (one for each injector) The ECU triggers the injectors sequentially following the firing order of the engine so that the fuel is sprayed into each intake port as the valve for that cylinder is opening. Fuel quantity is regulated by varying the duration (length of time) that the injectors are open.

Series Resistors (MPI Engine Management System):

This type of injector consists of a solenoid valve and a ball type nozzle. The solenoid is a low impedance type (internal resistance approx. 1 - 3 ohms), and requires an external resistor in series with each injector to regulate current. A resistor pack, which contains a resistor with approx. 5 - 7 ohms resistance for each injector, is mounted near the windshield wiper motor so the total resistance in each injector circuit is 6 - 10 ohms.
Each injector has an inlet and an outlet. Fuel constantly flows through the injector close to the nozzle to help keep it cool and reduce the tendency for fuel to percolate inside at high engine temperatures. Injectors are installed in the intake manifold where the manifold joins to the cylinder head. Injectors are sealed by O-rings and held in place by the fuel rail.