Fuel Metering System

The function of the fuel metering system is deliver the correct amount of fuel to the engine under all operating conditions. Fuel is delivered to each cylinder by the fuel injectors. The fuel injectors are controlled sequentially by the Powertrain Control Module (PCM). The PCM bases the control of the fuel injectors on several important engine parameters.

The two most important inputs for fuel control are the Mass Air Flow (MAF) sensor and the heated oxygen sensor 1 (HO2S 1). The MAF sensor provides the Powertrain Control Module (PCM) with engine air intake quantity, while the HO2S 1 provides the PCM with exhaust stream oxygen content information. Determining air density is critical to proper air/fuel management. Air density is primarily derived from the MAF sensor input. The MAF sensor measures the air volume and determines the air density. Larger volumes of air and denser air masses require additional fuel. The information from the MAF sensor is used by the PCM in order to modify the fuel injector pulse width.

The PCM modifies the air/fuel mixture by changing the injector pulse width signal sent to the injectors. By constantly measuring the air intake and the exhaust oxygen content and adjusting the injector pulse width, the air fuel ratio is kept very close to the optimal 14.7:1. This is the range at which the Three-Way Catalytic Converter (TWC) operates most effectively and at which the emissions of this vehicle are kept to a minimum. The constant tailoring of the air/fuel ratio is based upon feedback from the HO2S 1 and is referred to as closed loop operation.