Fuel Charging and Controls
Fuel Delivery Components:
Sequential Multiport Fuel Injection (SFI)
WARNING: DO NOT SMOKE OR CARRY LIGHTED TOBACCO OR OPEN FLAME OF ANY TYPE WHEN WORKING ON OR NEAR ANY FUEL-RELATED COMPONENT. HIGHLY FLAMMABLE MIXTURES ARE ALWAYS PRESENT AND MAY BE IGNITED, RESULTING IN PERSONAL INJURY.
The sequential Multiport Fuel Injection (SFI) system is classified:
^ multi-point
^ pulse time
^ mass airflow
^ fuel injection system
Fuel is metered into each intake port in a sequential firing order. Fuel injectors pulse to follow engine firing order in accordance with engine demand on a tuned intake manifold.
The basic fuel requirement of the engine is determined from the data supplied to the Powertrain Control Module (PCM) by the Mass Air Flow (MAF) sensor, which measures the amount of air being drawn into the engine.
Other sensors are used to measure:
^ air temperature
^ engine coolant temperature
^ engine speed
^ exhaust oxygen content
The various sensors detect any changes in the operating conditions and send signals to the powertrain control module. This permits the powertrain control module to control the opening duration (pulse width) of the fuel injectors and maintain optimum exhaust emission control and engine performance for all operating conditions.
For more information on the fuel pump, fuel tank, fuel lines, and the fuel filter, please refer to each individual component.
The fuel injection supply manifold incorporates the electrically actuated fuel injectors directly above each of the engine intake ports. The fuel injectors, when energized, provide fuel into the intake air stream.
A constant fuel pressure drop is maintained across the fuel injectors by the fuel pressure regulator.
^ The fuel pressure regulator is attached to the fuel injection supply manifold and positioned downstream from the fuel injectors.
^ On a returnless fuel system, excess fuel supplied by the fuel pump, but not required by the engine, passes through the fuel pressure regulator located in the fuel tank. Excess fuel is diverted to the fuel tank.
Fuel Injection Timing
The period of time the fuel injectors are energized is controlled by the powertrain control module.
The pulse width is determined by inputs from the:
^ Heated Oxygen Sensor (HO2S)
^ mass air flow sensor
^ Engine Coolant Temperature (ECT) sensor
^ camshaft synchronizer
^ Intake Air Temperature (IAT) sensor
^ Between idle and 6,500 rpm, the fuel is injected to each cylinder independently by giving one injection per two crankshaft rotations (one injection per cycle) to all cylinders.
^ Fuel injection for each cylinder takes place during its exhaust stroke.
^ Above 6,500 rpm, fuel is cut to prevent engine overspeeding and possible engine damage.
Air Induction System
The air induction system supplies filtered air to the engine to mix with the fuel for combustion purposes.
^ the air induction system consists of an engine air cleaner intake tube and duct, air cleaner assembly with filter, air cleaner outlet tube, mass air flow sensor, and combined throttle body and intake plenum.
Throttle Body
The throttle body controls airflow to the engine through a single butterfly-type valve.
^ the throttle position is controlled by a conventional cable through throttle linkage.
^ the body is a single-piece die casting made of aluminum and has a single bore with an air bypass channel around the throttle plate.
^ this bypass channel provides engine idle control is regulated by an Idle Air Control (IAC) valve assembly mounted directly to the throttle body.
^ the valve assembly is an electromechanical device controlled by the powertrain control module which incorporates a linear actuator which positions a variable area metering valve.
^ a sealant is applied to the throttle plate and bore area to reduce closed plate-to-bore airflow. The sealant should not be removed or cleaned.
Other features of the throttle body include:
^ factory-set throttle plate position at idle. DO NOT adjust or tamper with the throttle return control screw unless required by the Powertrain Management.
^ a preset stop to locate the wide-open throttle position.
^ a throttle body-mounted Throttle Position (TP) sensor.
^ provision for Exhaust Gas Recirculation (EGR) valve.
^ individual vacuum taps required for PCV, EVAP and vacuum sensing EEC sensors and controls.
Throttle Body and Upper Intake Manifold
The throttle body is integrated into a single aluminium casting.
^ runner lengths are tuned to optimize the engine torque and power output.
^ the throttle body provides mounting flanges for the accelerator control bracketry and the EGR valve.
^ vacuum taps are provided to supply various engine accessories.
Lower Intake Manifold
The lower intake manifold contains machined pockets for the fuel injectors to prevent air and fuel leakage.
^ The pockets in which the fuel injectors are mounted are placed to direct the fuel spray immediately in front of each engine intake valve.
Fuel Pump
The fuel system:
^ uses an electric fuel pump to provide high-pressure fuel to the fuel injectors.
^ is located at the rear of the vehicle and is mounted in the fuel tank.
^ has a fuel pressure regulator located in the fuel tank which separates the excess fuel supplied by the fuel pump directly to the fuel tank.
^ the fuel tubes leading from the fuel tank to the engine are under pressure during vehicle operation.
^ when the engine is turned off, the fuel in the fuel tubes remains pressurized for long periods of time to provide quick start-ups.
^ For more information about the fuel tank, fuel filter, lines, and electric fuel pump, please refer to each individual component.
Fuel Injectors
The fuel injectors are electromechanical devices which both meter and atomize fuel delivered to the engine.
^ the MFI fuel injectors are mounted in the lower intake manifold.
^ the valve body consists of a solenoid actuated valve assembly; therefore, fuel flow to the engine is regulated only by how long the solenoid is energized.
^ an electrical signal from the powertrain control module activates the solenoid.
Fuel Injection Supply Manifold
The fuel injection supply manifold:
^ is the component that delivers high-pressure fuel from the vehicle fuel supply line to the six fuel injectors.
^ consists of a preformed tube or stamping with one connector for each fuel injectors,
^ has a mounting flange for the fuel pressure regulator
^ has a fuel pressure relief valve for diagnostic testing or field service fuel system pressure bleed-down, and mounting attachments which locate the fuel injection supply manifold and provide fuel injector retention.
Fuel Pressure Regulator
The fuel pressure regulator is attached to the fuel injection supply manifold downstream of the fuel injectors.
^ it regulates the fuel pressure supplied to the fuel injectors.
^ the fuel pressure regulator is a diaphragm-operated relief valve in which one side of the diaphragm senses fuel pressure and the other side is subjected to intake manifold vacuum. The nominal fuel pressure is established by a spring preload applied to the diaphragm. Balancing one side of the diaphragm with manifold pressure maintains a constant fuel pressure drop across the fuel injectors.
^ Fuel in excess of that used by the engine is bypassed through the fuel pressure regulator and returns to the fuel tank.
Fuel Pressure Relief Valve
The fuel pressure relief valve is used to relieve fuel pressure from the fuel system.
^ for fuel system pressure relief procedures, refer to Removal and Installation. Service and Repair
Fuel Charging Wiring (SFI)
A single engine control sensor wiring harness contains all wiring and connections for all engine-mounted sensors and fuel system control components. A 104-pin connector connects to the vehicle powertrain control module and a 42-pin connector connects engine components to other vehicle systems.
Inertia Fuel Shutoff (IFS) Switch
The inertia fuel shutoff switch (IFS switch):
^ is used in conjunction with an electric fuel pump.
^ shuts off the fuel pump in the event of a collision.
^ consists of a steel ball held in place by a magnet.
^ when a sharp impact occurs, the ball breaks loose from the magnet, rolls up a ramp and strikes a target plate which opens the electrical contacts of the inertia fuel shutoff switch and shuts off the fuel pump. Once the inertia fuel shutoff switch is open, it must be manually reset before restarting the vehicle.
Fuel Pump, Relay
The fuel pump relay supplies power to the fuel pump when the powertrain control module grounds the relay during START and engine RUNNING conditions.
A/C Compressor Clutch Control Relay
The A/C cutoff relay:
^ is used to improve idle smoothness after engine start-up and to improve acceleration performance.
^ the A/C is cut off for approximately 5 seconds under the following conditions: just after the engine is started, and when the throttle position sensor indicates a wide open throttle condition.