Fuel Delivery System

Intake Manifold Assembly:

PURPOSE
The function of the fuel metering system is to deliver the correct amount of fuel to the engine under all operating conditions.

OPERATION
Fuel is delivered to the engine by individual bottom feed type multiport fuel injectors mounted in the lower intake manifold near each cylinder.
The Powertrain Control Module (PCM) pulses the fuel injectors in pairs. Alternate pairs are pulsed every 180° of crankshaft revolution. This is called Alternating Synchronous Double Fire (ASDF) injection.
The PCM uses two injector driver circuits, each controlling a pair of injectors. The current in each circuit is allowed to climb to a peak of 4 amps and then is reduced to 1 amp to hold the injector open. This happens very quickly.

The main control sensor is the Oxygen Sensor (O2S) located in the exhaust manifold. This sensor indicates to the PCM how much oxygen is in the exhaust gas, and the PCM changes the air/fuel ratio to the engine by controlling the fuel injectors. The best mixture to minimize exhaust emissions is 14.7:1 which allows the catalytic converter to operate most efficiently. Because of the constant measuring and adjusting of the air/fuel ratio, the fuel injection system is called a "Closed Loop" system.

ALTERNATING SYNCHRONOUS DOUBLE FIRE (ASDF) FUEL INJECTION
For better fuel vaporization and improved emission control, fuel is injected at the intake valves while they are in the closed position. To do this, the fuel injectors are alternately pulsed in pairs. Injectors for cylinders 1 and 4 are electrically paired, as are the injectors for cylinders 2 and 3. Each pair of injectors is pulsed twice (double fire), once on the compression stroke and once on the exhaust stroke for each cylinder.

FUEL METERING SYSTEM COMPONENTS
The fuel metering system consists of the following parts:
^ Fuel supply components (fuel tank, pump, pipes).
^ Fuel pump electrical circuit.
^ Intake manifold assembly, consisting of:

- Lower manifold assembly, including:
^ MFI fuel injectors.
^ Fuel pressure regulator assembly.

- Upper manifold assembly, including:
^ Throttle valve.
^ Idle Air Control (IAC) valve.
^ Throttle Position (TP) sensor.

FUEL SUPPLY COMPONENTS
The fuel supply is stored in the fuel tank. An electrical fuel pump contained in the modular fuel sender assembly pumps fuel through an in-line fuel filter to the fuel rail assembly. The pump is designed to provide fuel at a pressure above the regulated pressure needed by the injectors.

Fuel is recirculated through the fuel rail continuously while the engine is running. This removes air and vapors from the fuel as well as keeping the fuel cool during hot weather operations.

The fuel pressure regulator that is mounted on the fuel rail, maintains a variable pressure across the injectors based on intake manifold vacuum (load). It is accomplished by controlling the amount of fuel that is recirculated back to the fuel tank.

Unleaded fuel must be used with all gasoline engines for proper emission control system operation. Using unleaded fuel will also decrease spark 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.

All vehicles with gasoline engines are equipped with an Evaporative Emission System that minimizes the escape of fuel vapors to the atmosphere.