General System Description

Fuel Metering System
The function of the fuel metering system is to deliver the correct amount of fuel to the engine under all operating conditions. Fuel is delivered to the engine by individual fuel injectors near each cylinder. The PCM uses voltage inputs from several sensors to determine how much fuel to give the engine. Each injector is energized individually in the engine firing order, which is called Sequential Fuel Injection (SFI). However, if the PCM loses voltage input from the Camshaft Position (CMP) Sensor, the PCM will energize the fuel injectors using the Alternating Synchronous Double Fire (ASDF) method. The main control sensor is the Oxygen Sensor (O2S) located in the exhaust manifold. This sensor indicates to the PCM how much oxygen is in the exhaust gas, and the PCM changes the air/fuel ratio to the engine by controlling the fuel injectors. The best mixture to minimize exhaust emissions is 14.6:1 which allows the catalytic converter to operate most efficiently. Because of the constant measuring and adjusting of the air/fuel ratio, the fuel injection system is called a Closed Loop system.

System Components
Fuel Metering System Components The fuel metering system is made up of the following parts:

^ Fuel supply components (fuel tank, pump, and lines).
^ Fuel pump electrical circuit.
^ Fuel rail assembly, including:
^ Fuel injectors.
^ Fuel pressure regulator.
^ Throttle body assembly, including:
- Idle Air Control (IAC) valve.
- Throttle Position (TP) sensor.