Fuel Delivery and Air Induction: Description and Operation
System Diagram:
This vehicle is equipped with a 3.0 liter, DOHC (four overhead camshafts, 2 per cyl. bank) 60° V6 cylinder gasoline engine, and a computer controlled sequential electronic fuel injection system. The system maintains an air/fuel mixture as close as possible to the ideal stoichiometric ratio. During normal operation, the computer operates the injectors sequentially according to the firing order, for varying lengths of time depending on the amount of fuel required.
FUEL INJECTION
Fuel is supplied to the fuel rail and injectors at high pressure by the fuel pump in the tank. A fuel pressure regulator varies fuel pressure slightly depending on manifold vacuum. When fuel demand is high as indicated by low manifold vacuum, the pressure is increased slightly. A pulsation damper helps to reduce fuel pressure oscillations from the pump. The injectors are electric solenoid valves that get power when the engine is cranking or running and turn "ON" when the Powertrain Control Module (PCME) completes their circuits to ground. Injectors spray fuel into the intake port when they are turned "ON". The amount of fuel sprayed depends on the injector "pulse width" (length of time the injectors are turned "ON" during each injection cycle). Injectors are operated sequentially, which means each injector turns on when the intake valve for that cylinder is opening.
STARTING AND WARM-UP
During cranking when the engine is cold, a cold start injector sprays additional fuel into the intake manifold dynamic chamber to provide a richer mixture for easy starting. When the engine is running cold, the fuel injection system operates in what is known as "OPEN LOOP" mode. In this mode, the PCME determines the amount of fuel needed depending on the engine coolant temperature and the amount of air flow as measured by the air flow meter. A specific pulse width is assigned for certain air flow rates at various temperatures. These are the "base" pulse width values stored in the computer memory which provide a slightly rich air/fuel ratio for good driveability while the engine is cold and during warm-up.
NORMAL WARM ENGINE OPERATION
When the engine warms up, the fuel injection system switches to "CLOSED LOOP" operation. In this mode, the computer monitors several sensors in addition to the air flow meter and temperature sensor, including an exhaust gas oxygen sensor. Signals from the oxygen sensor tell the PCME if the air/fuel ratio is rich or lean. The PCME then modifies the base pulse width accordingly to increase or decrease the amount of fuel being injected, depending on the need at that moment.
IDLE SPEED CONTROL
The idle speed is controlled by the Bypass Air Control (BAC) valve. Depending on engine temperature and signals from the PCME, the BAC valve regulates how much measured air is allowed to bypass the throttle valves. The BAC valve has two parts; the air valve is open when cold and the idle air control valve is electrically operated by the PCME. In the air valve, a temperature sensitive wax pellet is heated by engine coolant. As the engine warms up, the pellet expands against the air valve, closing it. When the engine is warm, idle speed is controlled by the PCME through signals to the idle air control valve.
DECELERATION FUEL CUT-OFF
The PCME recognizes when the engine is decelerating by monitoring the engine speed and an idle switch that tells the PCME when the throttle is closed. When the throttle is closed and engine rpm is above a certain speed, the PCME will cut injection to reduce emissions and improve fuel economy.
INTAKE AIR SYSTEM - VARIABLE INERTIA CHARGING SYSTEM (VICS)
Variable Inertia Charging System (VICS):
The intake manifold has long and short air pathways. The two are separated by a shutter valve similar to a throttle valve in each intake runner. When the shutter valves are closed, air must take the long path. When the valves are open, air takes the shorter path. Shutter valves are opened and closed at different engine speeds to take advantage of harmonic oscillations in the intake manifold runners. This helps "pack" more fuel and air into the cylinders during each cylinder cycle (improved volumetric efficiency), increasing torque and horsepower over a broader rpm range.
FUEL AND INTAKE SYSTEM COMPONENTS
^ Accelerator pedal and cable
^ Air cleaner, intake air ducts, intake manifold, and associated parts
^ Bypass air control valve
- Air valve
- Idle speed control (ISC) valve
^ Cold start injector
^ Fuel tank
^ Fuel pump
^ Fuel pump relay
^ Fuel filter
^ Fuel pressure regulator
^ Fuel rail
^ Fuel hoses
^ Fuel injectors
^ Pulsation damper
^ Shutter valves and actuator (Variable Inertia Charging System - VICS)
^ Throttle body
^ Vacuum reservoir and check valve (VICS)