The function of the fuel and air control system is to manage the fuel and the air delivery to each cylinder to optimize the performance and the driveability of the engine under all of the driving conditions. The fuel supply is stored in a High Density Polyethylene (HDPE) fuel tank located behind the rear wheels. The fuel sender allows retrieval of fuel from the tank and also provides information on the fuel level. An electric fuel pump contained in the modular fuel sender pumps the fuel through the nylon lines and an in-line fuel filter to the fuel rail. The pump is designed to provide the fuel at a pressure above the regulated pressure which is needed by the injectors. The fuel is then distributed through the fuel rail to six injectors inside of the intake manifold. The fuel pressure is controlled by a pressure regulator that is mounted on the fuel rail. The fuel system in this vehicle is recirculating. This means that any excess fuel that is not injected into the cylinders is sent back to the fuel tank by a separate nylon line. This removes any air and any vapors from the fuel as well as keeping the fuel cool during hot weather operation. Each fuel injector is located directly above each cylinder's two intake valves. The accelerator pedal in the passenger compartment is linked to the throttle valve in the throttle body by a cable. The throttle body regulates the air flow from the air cleaner into the intake manifold, which then distributes this air to each cylinder's two intake valves. This allows the driver to control the air flow into the engine, which then controls the power output of the engine.

Unleaded fuel must be used with all of the gasoline engines for a proper emission control system operation. Using unleaded fuel will also minimize any spark plug fouling and extend the engine oil life. Leaded fuel can damage the emission control system, and use of unleaded fuel can result in loss of emission warranty coverage.

All vehicles with gasoline engines are equipped with an Evaporative Emission Control (EVAP) System that minimizes the escape of fuel vapors to the atmosphere.

The Catera engine is fueled by six individual injectors, one for each cylinder, that are controlled by the ECM. The ECM controls each injector by energizing the injector coil for a brief period once every other engine revolution. The length of this brief period, or pulse, is carefully calculated by the ECM to deliver the correct amount of fuel for proper driveability and emissions control. The length of time that the injector is energized is called the pulse width and is measured in milliseconds (thousandths of a second).

While the engine is running, the ECM is constantly monitoring the inputs and recalculating the appropriate pulse width for each injector. The pulse width calculation is based on the injector flow rate (mass of fuel the energized injector will pass per unit of time), the desired air/fuel ratio, and actual air mass in each cylinder and is adjusted for battery voltage, short term and long term fuel trim. The calculated pulse is timed to occur as each cylinders intake valves are closing to attain largest duration and most vaporization.

Fueling during a crank is slightly different than fueling during an engine run. As the engine begins to turn, a prime pulse may be injected to speed starting. As soon as the ECM can determine where in the firing order the engine is, the ECM begins pulsing the injectors. The pulse width during the crank is based on the coolant temperature and the engine load.

The Catera fueling system has several automatic adjustments in order to compensate for the differences in the fuel system hardware, the driving conditions, the fuel used, and the vehicle aging. The basis for the fuel control is the pulse width calculation that is described above. Included in this calculation are an adjustment for the battery voltage, the short term fuel trim, and the long term fuel trim. The battery voltage adjustment is necessary since the changes in the voltage across the injector affect the injector flow rate. The short term and the long term fuel trims are fine and gross adjustments to the pulse width that are designed in order to maximize the driveability and emissions control. These fuel trims are based on the feedback from the oxygen sensors in the exhaust stream and are only used when the fuel control system is in a closed loop operation.

Under certain stringent conditions, the fueling system will not energize the injectors, individually or in groups, for a period of time. This is referred to as the Fuel shut-off. The Fuel shut-off is used in order to improve the traction, save fuel, improve the starting, and protect the vehicle under certain extreme or abusive conditions.

Notice: Do not operate the engine in the back-up fuel for extended periods. Back-up fueling will negatively impact driveability and fuel economy, and may cause damage to the emissions system.

In case of a major internal problem, the ECM is equipped with a back-up fueling system that will run the engine until service can be performed.

The ECM controls the fuel injectors based on information that the ECM receives from several information sensors. Each injector is fired individually in the engine firing order, which is called a Sequential Multiport Fuel Injection. This allows precise fuel metering to each cylinder and improves the driveability under all of the driving conditions.