See Figure 1
The Multi-port Fuel Injection (MFI) system is a fuel metering system where the amount of fuel delivered by the injectors is determined by an electronic signal supplied by the Electronic Control Module (ECM). The ECM monitors various engine and vehicle conditions to calculate the fuel delivery time (pulse width) of the injectors. The fuel pulse may be modified by the ECM to account for special operating conditions, such as cranking, cold starting, altitude, acceleration, and deceleration.
The ECM controls the exhaust emissions by modifying fuel delivery to achieve, as near as possible, an air/fuel ratio of 14.7:1. The injector on-time is determined by various inputs to the ECM. By increasing the injector pulse, more fuel is delivered, enriching the air/fuel ratio. Decreasing the injector pulse leans the air/fuel ratio.
Each fuel injector (one per cylinder) is a solenoid-operated device controlled by the ECM. The incoming fuel is directed to the lower end of the injector assembly which has a fine screen filter surrounding the injector inlet. The ECM actuates the solenoid, which lifts a normally closed pintle off a seat. The fuel, under pressure, is injected in a conical spray pattern just above the intake valve. The excess fuel passes through a pressure regulator before being returned to the vehicle's fuel tank.
The pressure regulator is a diaphragm-operated relief valve. The function of the regulator is to maintain a constant pressure drop across the injector throughout the operating load and speed range of the engine.