The fuel rail design utilizes top-feed fuel injectors for fuel delivery. The fuel rail attaches to the intake manifold without the use of bolts.

The fuel rail is mounted to the top of the engine and distributes fuel to the six individual fuel injectors. The fuel is delivered to the fuel inlet tube 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 fuel in excess of the injector needs flows through the pressure regulator assembly to the outlet port of the fuel rail and through the fuel return pipe to the fuel tank to begin the cycle again. The fuel pressure can be observed using a fuel pressure gauge at the fuel pressure gauge connection.

An 8-digit identification number is stamped on the fuel rail assembly. The model identification number contains the Julian date, the year, and the shift. Refer to this model identification number if any service or a part replacement is required.

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 it to become further atomized and vaporized before entering the combustion chamber.

The eight digit part number (2) is identified on the fuel injector body (1). A four digit number 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 284-325 kPa (41-47 psi), adjusted for 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, in to decrease the air flow or out to increase the air flow, a controlled amount of air can move around the throttle plate. If the 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 a decreased 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 drops below 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 to prevent a stall.

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

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

The IAC 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 the 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. A 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. A DTC P0506 may set. If the IAC pintle is stuck part way 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. It senses 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 (pulse). For further information, Refer to Information Sensors/Switches Description .

The MAF sensor is attached to the front (air inlet side) 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 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 two seconds to build up the fuel pressure quickly. If the engine is not started within two 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 to energize the electric 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.

The PCM receives data from various information sensors, determines the required fuel and idle speed values, and then controls the IAC valve, the 6 fuel injectors, and the spark advance to maintain the optimum performance and driveability under all driving conditions. For more information on the PCM, refer to Powertrain Control Module Diagnosis .