The fuel metering system is made up of the following parts:

The fuel metering system starts with the fuel in the fuel tank. An electric fuel pump, which is 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 of more than 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 the fuel tank, the in-pipe filter, and the fuel pipes, refer to Fuel Supply Component Description .

The accelerator control system is a cable-type. There are no linkage adjustments. Therefore, the specific accelerator control cable must be used.

The throttle body has a throttle plate to control the amount of air delivered to the engine. The throttle position (TP) sensor (2), and idle air control (IAC) sensor (1) are also mounted on the throttle body.

Vacuum ports located behind the throttle plate provide the vacuum signals needed by various components.

The fuel rail assembly is made up of the left fuel rail (5), which delivers fuel to the even-numbered cylinders (2,4,6), the right fuel rail (1), which delivers fuel to the odd-numbered cylinders (1,3,5), the fuel injectors (4), and the fuel pressure regulator assembly (3), and distributes fuel to the cylinders through the individual injectors.

Fuel is delivered to the fuel inlet tube (2) of the fuel rail by the fuel pipes. The fuel then goes through the fuel rail to the fuel pressure regulator. The fuel pressure regulator maintains a constant fuel pressure at the fuel injectors. Any remaining fuel is then returned to the fuel tank.

The MULTEC 2 MPFI fuel injector assembly is a solenoid operated device, controlled by an on-board computer called the powertrain control module (PCM) that meters fuel to a single engine cylinder. The PCM energizes the high-impedance (12.0 ohms) solenoid (2) to open a normally closed ball valve (3). This allows fuel to flow into the top of the injector (1), past the ball valve, and through a director plate at the injector outlet. The director plate has precision holes that control fuel flow, generating a spray of finely atomized fuel at the injector tip. Fuel from the injector tip is directed at the intake valve, causing the fuel to become further atomized and vaporized before entering the combustion chamber.

The 8-digit part number (2) is identified on the fuel injector body (1). A 4-digit build date code is located to the far left of the part number.

The fuel pressure regulator is a diaphragm-operated relief valve with fuel pump pressure on one side and manifold pressure on the other. The function of the fuel pressure regulator is to maintain the fuel pressure available to the fuel injectors at 3 times the barometric pressure, when adjusted for the engine load.

The fuel pressure regulator is mounted on the fuel rail and may be serviced separately.

If the fuel pressure is too low, poor performance and DTC P0171 could result. If the pressure is too high, excessive odor and/or DTC P0172 may result. Refer to Fuel System Pressure Test .

The purpose of the idle air control (IAC) valve is to control the engine idle speed while preventing stalls due to changes in the engine load. The IAC valve, mounted in the throttle body, controls the bypass air around the throttle plate. By moving a conical valve, known as a pintle, inward to decrease the air flow or outward to increase the air flow, a controlled amount of air can move around the throttle plate. If RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate and an increased RPM. If RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate and decreasing the RPM.

The IAC pintle moves in small steps called "counts."

During idle, the proper position of the IAC pintle is calculated by the PCM based on the battery voltage, the engine coolant temperature, the engine load, and the engine RPM. If the RPM decreases to less than a specified value and the throttle plate is closed, the PCM senses a near-stall condition. The PCM will then calculate a new IAC pintle position in order to prevent stalls.

If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset.

The IAC resets when the key is cycled ON then OFF.

When servicing the IAC, the valve should only be disconnected or connected with the ignition OFF in order to keep from having to reset the IAC.

The position of the IAC pintle affects engine start-up and the idle characteristics of the vehicle. If the IAC pintle is open fully, too much air will be allowed into the manifold. This results in a high idle speed, along with possible hard starting and a lean air/fuel ratio. DTC P0507 may set. If the IAC pintle is stuck closed, too little air will be allowed into the manifold. This results in a low idle speed, along with possible hard starting and a rich air/fuel ratio. DTC P0506 may set. If the IAC pintle is stuck partly open, the idle may be high or low and will not respond to changes in the engine load.

The non-adjustable TP sensor is mounted on the side of the throttle body opposite the throttle lever. The TP sensor determines the throttle valve angle and relays that information to the PCM. Knowledge of the throttle angle is needed by the PCM to generate the required injector control signals. For further information, refer to Information Sensors/Switches Description .

The MAF sensor is attached to the front of the throttle body and is used to measure the amount of air entering the engine. The PCM uses this information to determine the operating condition of the engine and to control the fuel delivery. For further information, refer to Information Sensors/Switches Description .

When the key is first turned ON, the PCM energizes the fuel pump relay for 2 seconds in order to build up the fuel pressure quickly. If the engine is not started within 2 seconds, the PCM shuts the fuel pump OFF and waits until the engine is cranked. When the engine is cranked and the RPM signal has been detected by the PCM, the PCM supplies 12 volts to the fuel pump relay in order to energize the in-tank fuel pump.

An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold.

An inoperative fuel pump would cause a no-start condition. A fuel pump which does not provide enough pressure can result in poor performance.