The FLVV (1) on the FWD vehicle is an integral part of the EVAP canister (3). The cross sectional view shows the path of fuel vapors passing thru the valve directly into the EVAP canister. When the fuel filler cap is removed during refueling, the atmosphere chamber (2) fills with atmospheric pressure that has entered thru the port from the fuel filler pipe. The pressure in the atmosphere chamber (2) opens the passage to the vapor chamber (5) by opening the vent control valve (6). Refueling causes the internal pressure in the fuel tank to increase, pushing fuel vapors into the ORVR port (4) and up thru the vent control valve (6) into the EVAP canister (3). When the fuel tank is full, the tank vapor control valve (5) closes, sealing off the passage into the EVAP canister.

The accelerator control system on the 1.8L-LV6 vehicle with AWD is cable-operated. When the accelerator pedal is depressed the cable pulls the throttle lever open, increasing the throttle plate opening, and when the accelerator pedal is released, the throttle lever spring pressure returns the throttle lever to the idle position, decreasing the throttle plate opening.

An electronic throttle control (ETC) system or throttle actuator control (TAC) system is used to control the throttle on the 1.8L-LV6 vehicle with FWD. For information about the operation of the TAC system, refer to Throttle Actuator Control (TAC) System Description.

The function of the fuel metering system is deliver the correct amount of fuel to the engine under all operating conditions. Fuel is delivered to each cylinder by the fuel injectors. The fuel injectors are controlled sequentially by the powertrain control module (PCM). The PCM bases the control of the fuel injectors on several important engine parameters. These engine parameters include the following:

Determining air density is critical to proper air/fuel management. Air density is primarily derived from the MAF sensor input. The mass air flow (MAF) sensor measures the air volume and determines the air density. Larger volumes of air and denser air masses require additional fuel. The information from the MAF sensor is used by the PCM in order to modify the fuel injector pulse width.

The fuel injector (1) is an electromagnetic (solenoid) type injection nozzle which injects fuel into the intake port of the cylinder head according to the signals from the powertrain control module (PCM). There are 4 fuel injectors, one for each cylinder, located between the intake manifold and the fuel rail.

The PCM energizes the solenoid coil of the fuel injector (1), generating an electromagnet field that attracts the solenoid plunger (2). The needle valve, which is incorporated with the solenoid plunger (2), is opened by the movement of the solenoid plunger (2). The opening of the needle valve allows fuel that is under pressure to disperse through a 12-hole plate (3) into a cone shaped pattern. Because the stroke of the needle valve in the fuel injector is set constant, the amount of fuel injected at one time is determined by the pulse width injection time, the length of time the solenoid coil is energized.

The PCM controls the amount of fuel the fuel injector supplies to each cylinder by controlling the ON time, or length of pulse, of each individual injector. The delivery timing of the fuel into the cylinder head intake port by the fuel injector is controlled by the PCM. The timing and pulse of the fuel injectors is carefully calculated with inputs from the various sensors so that a suitable air/fuel mixture is supplied to the engine for every driving condition.

There are two types of injection timing. One is synchronous injection, when fuel injection is synchronous with the ignition signal or the signal from the camshaft position (CMP) sensor. The other is asynchronous injection, when fuel injection takes place independently of the ignition signal or the signal from the CMP sensor.

The PCM first calculates the correct timing of the fuel injectors by factoring the engine speed and the air volume together. Then the PCM applies certain compensations that are based on the information provided by various sensors which detect the state of the engine and the current driving conditions.

When starting the engine, the fuel injectors inject the fuel simultaneously and synchronously at every camshaft position (CMP) sensor signal. When the engine is starting at a cold state, the amount of fuel is determined by the engine coolant temperature (ECT) sensor and is divided and injected.

Once the engine is running, the fuel injection occurs in a cylinder only when the cylinder is in the exhaust stroke. The PCM detects the compression stroke of cylinder 1 through the CMP sensor signal.

Whenever a change in the throttle valve opening exceeds a specified value, as determined by the PCM, additional fuel is injected simultaneously into the cylinders which are in the intake and exhaust strokes. This is in addition to the above synchronous injection and is not based on the ignition signal.

In order to improve starting performance, fuel enrichment during start up is carried out. For a certain time after the engine is started, the air/fuel mixture is enriched slightly in order to stabilize the engine speed. The amount of compensation varies depending on the engine coolant temperature as measured by the ECT sensor.

When the engine is cold, additional fuel is added in order to ensure good driveability. The level of enrichment of the air/fuel mixture is gradually decreased until the engine coolant temperature (ECT) sensor reaches a specified value.

During acceleration, the pulse of the fuel injectors is lengthened in order to deliver more fuel. The additional fuel required is relative to the engine coolant temperature. Acceleration Enrichment ensures smooth and reliable engine acceleration.

In order to provide maximum power during high engine load driving conditions, the air/fuel mixture is enriched when the throttle valve opening is more than a specified, PCM determined, value.

A power supply system voltage drop will delay the mechanical operation of the fuel injector. The actual injector ON time becomes shorter when the system voltage decreases. In order to compensate for this, the fuel injector pulse width signal is lengthened.

The crank signal is sent from the starter motor circuit. When the starter motor circuit is energized as the ignition switch is in the START position, a crank signal is supplied to the PCM. The PCM increases the fuel injector pulse when receiving a voltage on the crank signal circuit. The slight increase in fuel provides quicker and smoother engine start-up. The crank signal is also used as an input for running certain engine control system diagnostics, such as the CKP sensor DTC P0335. The crank signal input can be monitored on a scan tool as the Starter Switch parameter.

The base air/fuel ratio may vary due to differences in individual engines and mileage. In order to compensate for such variations, feedback information is used to adjust the base air/fuel mixture to maintain the optimum air/fuel ratio.

Fuel cutoff occurs when the PCM stops fuel injection or turns off the fuel pump. Fuel cutoff is used during the following conditions:

In order to obtain the most efficient engine performance with a good balance of power and fuel economy, the air/fuel mixture must be kept as close to the theoretical air/fuel ratio of 14.7:1 as possible. Maintaining the 14.7:1 air/fuel ratio also provides efficient operation of the 3-way catalytic converter (TWC) and a high clarification rate of CO, HC and NOx in the exhaust gas stream, In order to accomplish this the PCM first compares the input voltage from the heated oxygen sensor 1 (HO2S 1) with a specified reference voltage.

The HO2S 1 sensors are a wide band or wide range design. As with all oxygen sensors, the wide band HO2S measures the amount of oxygen in the exhaust system, but provides more information than the typical switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The powertrain control module (PCM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the PCM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The PCM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the PCM can determine the concentration of oxygen in the exhaust. The HO2S input signal is displayed as a voltage within the range of 1-5 volts, with a steady value of 3.2-3.3 volts equal to the air fuel ratio of 14.7:1. If the HO2S 1 input voltage is lower than the specified reference voltage, the PCM determines that the air/fuel ratio is richer than the theoretical air/fuel ratio and reduces the fuel. If the input voltage from the HO2S 1 is higher than the specified reference voltage, the PCM determines that the air/fuel ratio is leaner and increases the fuel. By repeating these operations, the PCM can adjust the air/fuel ratio in order to be closer to the theoretical air/fuel ratio. Control of the fuel delivery system as just described is known as Closed Loop operation.

The HO2S signal is also displayed as a lambda value. A lambda value of 1 is equal to the stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the fuel system is lean and the oxygen level high, the lambda signal will be high or more than 1. When the fuel system is rich and the oxygen level low, the lambda signal will be low or less than 1.

The Closed Loop fuel control operation will not take place under any of the following conditions:

Control of the air supply that is mixed with the metered fuel is detailed in the description of the throttle actuator control (TAC) system and the air intake system. Refer to Throttle Actuator Control (TAC) System Description and Air Intake System Description.