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

When the ignition key is first turned ON, without the engine running, the PCM energizes the fuel pump relay for a calibrated time (approximately 2 seconds). This builds up fuel pressure quickly. Whenever the engine is not started within two seconds, the PCM shuts OFF the fuel pump and waits until ignition reference pulses are present. As soon as the engine is cranked, the PCM energizes the fuel pump relay which powers the fuel pump. An inoperative fuel pump relay or an inoperative fuel pump would cause a no start condition. A fuel pump which does not provide enough pressure can result in poor performance.

An eight digit identification number is stamped on the side of the fuel rail. Refer to this number if servicing or part replacement is required.

The fuel injector assembly is a solenoid-operated device, controlled by the PCM, that meters pressurized fuel to a single engine cylinder. The PCM energizes the fuel injector solenoid, which opens a ball valve, allowing fuel to flow past the ball valve, and through a recessed flow director plate at the injector outlet. The director plate has machined holes that control the fuel flow, generating a conical spray pattern of finely atomized fuel at the injector tip. Fuel from the tip is directed at the intake valve, causing it to become further atomized and vaporized before entering the combustion chamber. A fuel injector that is stuck partly open would cause loss of pressure after the engine is shut down, so long crank times would be noticed on some engines. Dieseling could also occur because some fuel could be delivered to the engine after the ignition is turned OFF.

The fuel pressure regulator assembly is a diaphragm-operated relief valve with fuel pump pressure on one side, and a regulator spring pressure and intake manifold vacuum on the other side. The regulator's function is to maintain a constant pressure differential across the injectors at all times. The pressure regulator compensates for engine load by increasing the fuel pressure as the engine vacuum drops. The fuel pressure regulator is serviced as a complete assembly. With the ignition ON and engine OFF (zero vacuum), fuel pressure should be 284-325 kPa (41-47 psi). Whenever the pressure is too low, poor performance and a DTC P0171 could result. Whenever the pressure is too high, excessive odor and a DTC P0172 could result.

The throttle body (1) assembly is attached to the intake manifold. The throttle body is used to control air flow into the engine, thereby controlling engine output. The throttle valve within the throttle body is opened by the driver through the accelerator controls. During engine idle, the throttle valve is almost closed, and air flow control is handled by the Idle Air Control (IAC) (3) .The throttle body also provides the location for mounting the Throttle Position (TP) (2) sensor and provides a manifold vacuum source for various components. Vacuum ports are located at the throttle valve to generate vacuum signals needed by various components.

Engine idle speed is controlled by the powertrain control module (PCM) through the IAC valve (1) mounted on the throttle body. The PCM sends voltage pulses to the IAC valve motor windings causing the IAC valve pintle (3) to move IN toward the seat, or OUT away from the seat, a given distance (a step, or count), for each pulse. The commanded location, steps away from the seated position, can be observed as a number of counts displayed on a scan tool. The pintle movement controls the airflow around the throttle valve (2), which in turn, controls engine idle speed:

The nonadjustable, throttle shaft-driven TP sensor is mounted on the throttle body assembly opposite the throttle cam lever. The TP sensor senses the throttle valve angle and relays the information to the Powertrain Control Module (PCM). Knowledge of throttle angle is needed by the PCM to properly control the injector control signals (pulses).