The fuel supply is stored in the fuel tank. An electric fuel pump attached to the fuel sender assembly (inside the fuel tank) pumps fuel through an in-line filter to the throttle body unit or fuel rail. The pump is designed to provide fuel at a pressure above the regulated pressure needed by the throttle body unit or fuel rail. Unused fuel is returned to the fuel tank by a separate pipe.
Unleaded fuel must be used with all gasoline engines for proper emission control system operation. Using unleaded fuel will also decrease spark plug fouling and extend engine oil life. Leaded fuel can damage the emission control system, and its use can result in loss of emission warranty coverage.
The function of the fuel and air control system is to manage fuel and air delivery to each cylinder to optimize the performance and driveability of the engine under all driving conditions. The fuel supply is stored in a High Density Polyethylene (HDPE) fuel tank (in late models) located behind the rear wheels. The fuel sender allows retrieval of fuel from the tank and provides information on fuel level.
An electric fuel pump, contained in the modular fuel sender, pumps fuel through nylon lines and an in-line fuel filter to the fuel rail. The pump is designed to provide fuel at a pressure above the regulated pressure needed by the injectors Fuel is then distributed through the fuel rail to six injectors inside the intake manifold. Fuel pressure is controlled by a pressure regulator mounted on the fuel rail. The fuel system is re-circulating; this means that excess fuel that is not injected into the cylinders is sent back to the fuel tank by a separate nylon line. This removes air and vapors from the fuel as well as keeping he fuel cool during hot weather operation. Each fuel injector is located directly above the two intake valves of each cylinder. The accelerator pedal in the passenger compartment is linked to the throttle valve in the throttle body by cable. The throttle body regulates airflow from the air cleaner into the intake manifold, which then distributes this air to the two intake valves of each cylinder. This allows the driver to control the airflow into the engine, which then controls the power output of the engine.
Unleaded fuel must be used with all gasoline engines for proper emission control system operation. Using unleaded fuel will also minimize spark plug fouling and extend engine oil life. Leaded fuel can damage the emission control system, and its use can result in loss of emission warranty coverage.
The Northstar engine is fueled by eight individual injectors, one for each cylinder, that are controlled by the PCM. The PCM controls each injector by energizing the injector coil for a brief period generally once every other engine revolution. The length of this brief period, or pulse, is carefully calculated by the PCM to deliver the correct amount of fuel for proper driveability and emissions control. The length of time the injector is energized is called the pulse width and is measured in milliseconds (thousandths of a second).
While the engine is running, the PCM is constantly monitoring its inputs and recalculating the appropriate pulse width for each injector. The pulse width calculation is based on the injector flow rate (mass or fuel the energized injector will pass per unit of time), the desired air /fuel ratio, and actual air mass in short term and long term fuel trim. The calculated pulse is timed to occur as the intake valves of each cylinder are closing to attain the largest duration and most vaporization.
Fueling during crank is slightly different than during engine run. As the engine begins to turn, a prime pulse may be injected to speed starting. As soon as the PCM can determine where in the firing order the engine is, it begins pulsing injectors. The pulse width during crank is based on coolant temperature and barometric pressure.
The Northstar fueling system has several automatic adjustments to compensate for differences in fuel system hardware, driving conditions, fuel used, and vehicle aging. The basis for fuel control is the pulse width calculation described above. Included in this calculation are an adjustment for battery voltage, short-term fuel trim, and long term fuel trim. The battery voltage adjustment is necessary since changes in voltage across the injector affect injector flow rate. Short term and long term fuel trims are fine and gross adjustments to pulse width designed to maximize driveability and emissions control. These fuel trims are based on feedback from oxygen sensors in the exhaust stream and are only used when the fuel control system is in closed loop.
Under certain stringent conditions, the fueling system will not energize injectors, individually or in groups, for a period of time. This is referred to as fuel shut-off. Fuel shut-off is used to improve traction, save fuel, improve starting, and to protect the vehicle under certain extreme or abusive conditions.