Fuel Delivery and Air Induction: Description and Operation
Fuel Control:
Fuel Delivery (Typical):
Emission Control Component Locations:
SYSTEM OPERATION
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.
COMPONENT OPERATION
Fuel Tank - The fuel supply is stored in a High Density Polyethylene (HDPE) fuel tank located in front of the rear wheels.
Fuel Sender - The fuel sender allows retrieval of fuel from the tank and also provides information on fuel level.
Fuel Pump - An electric fuel pump contained in the modular fuel sender pumps fuel through nylon pipes 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 Rail - Fuel is then distributed through the fuel rail to eight injectors inside the intake manifold.
Pressure Regulator - Fuel pressure is controlled by a pressure regulator mounted on the fuel rail. The fuel system in this vehicle is recirculating; this means that excess fuel that is not injected into the cylinders is sent back to the fuel tank by a separate nylon pipe, This removes air and vapors from the fuel as well as keeping the fuel cool during hot weather operation.
Fuel Injector - Each port fuel injector is located directly above each cylinder's two intake valves.
Throttle Cable - An accelerator pedal in the passenger compartment is linked to a throttle valve in the throttle body by a cable.
Throttle Body - The throttle body regulates 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.
Fuel - 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 fife. Leaded fuel can damage the emission control system, and its use can result in loss of emission warranty coverage. All cars with gasoline engines are equipped with an Evaporative Emission Control (EVAP) system that minimizes the escape of fuel vapors to the atmosphere.
SEQUENTIAL FUEL INJECTION
The PCM controls the fuel injectors based on information it receives from several information sensors. Each injector is fired individually in engine firing order, which is called Sequential Fuel Injection. This allows precise fuel metering to each cylinder and improves driveability under all driving conditions.
SPEED DENSITY FUEL CONTROL
The PCM uses a Speed/Density model to calculate the fuel required to maintain an Air/Fuel ratio of 14.7 to 1. This ratio is the optimum ratio of air to fuel required for lowest exhaust emissions (called the stoichiometric ratio). The Speed/Density model looks at engine speed and air density (calculated from MAP, IAT and ECT sensor information) to determine how much air is nowing into each cylinder. The PCM then calculates the length of time each injector must be turned on to provide the correct amount of fuel. This is called injector pulse width. The PCM looks at information from the 02 sensors to see if its injector pulse width is correct and makes adjustments as necessary.
MODES OF OPERATION
The PCM has several operating modes for fuel control, depending on the information it receives from the sensors.
STARTING MODE - When the key is first turned "ON", the PCM will turn "ON" the fuel pump relay for two seconds, The fuel pump runs and builds up pressure in the fuel system. The PCM then monitors the IAT, ECT, TP sensors and ICM signal to determine the required injector pulse width for starting.
CLEAR FLOOD MODE - If the engine is flooded with fuel during starting and will not start, CLEAR FLOOD MODE can be manually selected. To select CLEAR FLOOD MODE, push the accelerator to Wide Open Throttle (WOT). With this signal, the PCM will completely turn "OFF" the injectors and will maintain this as long as it sees a WOT condition with engine speed below 1000 rpm.
RUN MODE - The Run Mode has two conditions: "Open Loop" and "Closed Loop". When the engine is first started and engine speed is above 400 rpm, the system goes into "Open Loop" operation. In "Open Loop", the PCM ignores the signals from the O2 sensors and calculates the required injector pulse width based primarily on inputs from the IAT and ECT sensors.
The system will stay in "Open Loop" until the following conditions are met:
^ The 02 sensors have varying voltage output, showing that they are hot enough to operate properly.
^ The ECT sensor indicates above 80°C.
^ A calibrated time delay has elapsed after starting the engine. This delay allows all sensors to stabilize.
^ When these conditions are satisfied, the PCM goes into "Closed Loop" operation. In "Closed Loop", the PCM adjusts the calculated injector pulse width for each bank of injectors based on the signals from each 02 sensor.
ACCELERATION MODE - The PCM monitors changes in TP and MAP sensor signals to determine when the vehicle is being accelerated. The PCM will then increase injector pulse width to provide more fuel for improved driveability.
DECELERATION MODE - The PCM monitors changes in TP and sensor signals to determine when the vehicle is being decelerated. The PCM will then decrease injector pulse width or even shut "OFF" injectors for short periods to reduce exhaust emissions.
BATTERY VOLTAGE CORRECTION MODE - When the PCM sees a low battery voltage condition, it can compensate to maintain acceptable vehicle driveability. It does this by:
^ Increasing the injector pulse width to maintain the proper amount of fuel delivered.
^ Increasing the idle speed to increase generator output.
FUEL SHUT-OFF MODE - The PCM has the ability to completely turn all the injectors "OFF" or selectively turn "OFF" some of the injectors when certain conditions are met. These fuel shut-off modes allow the Northstar powertrain to protect itself from damage and also improve its driveability.
The PCM will disable all eight injectors under the following conditions:
^ Ignition "OFF" (prevents engine run-on).
^ Ignition "ON" but no ignition reference signal (prevents flooding or backfiring).
^ High engine speed (above red line).
^ High vehicle speed (above rated tire speed).
^ Extended high speed closed throttle coastdown. (reduces emissions and increases engine braking). The PCM will selectively disable up to six injectors under the following conditions.
^ Torque Management enabled (transaxle shifts or abusive maneuvers).
^ Traction Control enabled (in conjunction with front brakes applying).
^ Low coolant condition (protects engine from overheating).
SYSTEM COMPONENTS
^ Fuel tank
^ Fuel tank filler neck
^ Fuel filler cap
^ Modular fuel sender containing
- Fuel sender assembly
- Fuel pump
- Fuel strainer
- Fuel check valve
^ In-line fuel filter
^ Fuel and vapor pipes
^ Fuel pressure regulator
^ Fuel rail
^ Fuel injectors
^ Throttle body
^ Fuel pump relay
^ Powertrain Control Module and information sensors