Fuel Control System Operation Description
The function of the fuel metering system is to deliver the correct amount of fuel to the engine under all operating conditions. The fuel is delivered to the engine by the individual fuel injectors mounted into the intake manifold near each cylinder.
The two main fuel control sensors are the Manifold Absolute Pressure (MAP) sensor, the Heated Oxygen Sensor 1 (HO2S1) and the Heated Oxygen Sensor 2 (HO2S2).
The MAP sensor measures or senses the intake manifold vacuum. Under high fuel demands the MAP sensor reads a low vacuum condition, such as wide open throttle. The Engine Control Module (ECM) uses this information to richen the mixture, thus increasing the fuel injector on-time, to provide the correct amount of fuel. When decelerating, the vacuum increases. This vacuum change is sensed by the MAP sensor and read by the ECM, which then decreases the fuel injector on-time due to the low fuel demand conditions.
Fuel Injector Description
The Multiport Fuel Injection (MFI) assembly is a solenoid-operated device controlled by the Engine Control Module (ECM). It meters pressurized fuel to a single engine cylinder. The ECM energizes the fuel injector or the solenoid to a normally closed ball or pintle valve. This allows fuel to flow into the top of the injector, past the ball or pintle valve, and through a recessed flow director plate at the injector outlet.
The director plate has six machined holes that control the fuel flow, generating a conical spray pattern of finely atomized fuel at the injector tip. Fuel from the tip is directed at the intake valve, causing it to become further atomized and vaporized before entering the combustion chamber. A fuel injector which is stuck partially open will cause a loss of fuel pressure after the engine is shut down. Also, an extended crank time will be noticed on some engines. Dieseling can also occur because some fuel can be delivered to the engine after the ignition is turned OFF.