General Description

DESCRIPTION
The basic function of the air/fuel metering system is to control air/fuel delivery to the engine. The best air/fuel mixture to minimize exhaust emissions is 14.7 to 1, which allows the catalytic converter to operate most efficiently. Fuel is delivered to the engine by individual fuel injectors mounted in the intake manifold near each intake valve.

The main control sensor is the Heated Oxygen Sensor (HO2S), located in the exhaust manifold. The HO2S tells the Powertrain Control Module (PCM) how much oxygen is in the exhaust gas and the PCM changes the air/fuel ratio to the engine by controlling the fuel injector on time. Because of the constant measuring and adjusting of the air/fuel ratio, the fuel injection system is called a Closed Loop system.

The PCM monitors voltages from several sensors to determine the engine's fuel needs. Fuel is delivered under one of several conditions called modes. Refer to Fuel Metering Modes of Operation.

OPERATION
The fuel metering system starts with the fuel in the fuel tank. An electric fuel pump, located in the fuel tank with the gauge sending unit, pumps fuel to the fuel rail through an in-pipe fuel filter. The fuel pump is designed to provide fuel at a pressure above the pressure needed by the fuel injectors. A fuel pressure regulator in the fuel rail keeps fuel available to the fuel injectors at a constant pressure. Unused fuel is returned to the fuel tank by a separate pipe. For further information on these components, refer to Fuel Metering System Components.