The Multi-port Fuel Injection (MFI) system is electronically controlled by the Powertrain Control Module (PCM), based on data from various sensors. The PCM controls the fuel flow, idle speed and ignition timing.
Fuel is supplied to the injectors by an electric in-tank fuel pump and is distributed to the respective injectors via the main fuel pipe. The fuel pressure applied to the injector is constant and higher than the pressure in the intake manifold. The pressure is controlled by the fuel pressure regulator. The excess fuel is returned to the fuel tank through the fuel return pipe.
When an electric current flows in the injector, the injector valve is fully opened to supply fuel. Since the fuel pressure is constant, the amount of the fuel injected from the injector into the manifold is increased or decreased in proportion to the time the electric current flows. Based on PCM signals, the injectors inject fuel to the cylinder manifold ports in firing order.
Air enters the air intake plenum or manifold through the throttle body. In the intake manifold, the air is mixed with the fuel from the injectors and is drawn into the cylinder. The air flow rate is controlled according to the degree of the throttle valve and the servo motor openings.
The system is monitored through a number of sensors which feed information on engine conditions and requirements to the PCM. The PCM calculates the injection time and rate according to the signals from the sensors.