The throttle body contains a dual throttle valve which controls the amount of air that is being delivered to the engine. A coolant passage under the throttle valve heats the throttle body.

The fuel pump relay allows the ECM to energize the fuel pump. The ECM enables the fuel pump whenever the crankshaft position (CKP) sensor pulses are detected.

The function of the fuel and air control system is to manage the fuel and the air delivery to each cylinder, optimizing the performance and the driveability of the engine under all driving conditions. The fuel supply is stored in the 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 cylinders two intake valves. The throttle body regulates the air flow from the air cleaner into the intake manifold, which then distributes this air to each cylinders two intake valves.

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 leaded fuel can result in loss of emission warranty coverage.

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 period of time when 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.

In case of a major internal problem, the ECM is equipped with a back-up fuel strategy for limp in mode that will run the engine until service can be performed.

The engine control module (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.

The engine control module (ECM) has several operating modes for fuel control, depending on the information that has been received from the sensors.

When the ECM detects reference pulses from the crankshaft position (CKP) sensor, the ECM will enable the fuel pump. The fuel pump runs and builds up pressure in the fuel system. The ECM then monitors the mass air flow (MAF), intake air temperature (IAT), engine coolant temperature (ECT), and the throttle position (TP) sensor signal in order to determine the required injector pulse width for starting.

If the engine is flooded with fuel during starting and will not start, the Clear Flood Mode can be manually selected. To select Clear Flood Mode, push the accelerator to wide open throttle (WOT). With this signal, the ECM will completely turn OFF the injectors and will maintain this stage as long as the ECM indicates a WOT condition with engine speed below 1,000 RPM.

The Run Mode has 2 conditions: Open Loop operation and Closed Loop operation. When the engine is first started and the engine speed is above 480 RPM, the system goes into an Open Loop operation. In an Open Loop operation, the ECM ignores the signals from the oxygen sensors and calculates the required injector pulse width based primarily on inputs from the mass air flow (MAF), intake air temperature (IAT) and engine coolant temperatures (ECT) sensors.

In a Closed Loop, the ECM adjusts the calculated injector pulse width for each bank of injectors based on the signals from each oxygen sensor.

The ECM monitors the changes in the throttle position (TP) and the MAF sensor signals in order to determine when the vehicle is being accelerated. The ECM will then increase the injector pulse width in order to provide more fuel for improved driveability.

The ECM monitors changes in TP and MAF sensor signals to determine when the vehicle is being decelerated. The ECM will then decrease injector pulse width or even shut OFF injectors for short periods to reduce exhaust emissions.

The ECM can compensate in order to maintain acceptable vehicle driveability when the ECM sees a low battery voltage condition. The ECM compensates by performing the following functions:

The ECM has the ability to completely turn OFF all of the injectors or selectively turn OFF some of the injectors when certain conditions are met. These fuel shut-off modes allow the ECM to protect the engine from damage and also to improve the vehicles driveability.

The ECM will disable all of the six injectors under the following conditions:

The ECM will selectively disable the injectors under the following conditions: