Fuel System, Described 

Operation

An on-board vehicle powertrain control module (PCM):

• receives inputs from various electronic engine control sensors to compute the fuel flow rate  necessary to maintain a prescribed air/fuel ratio throughout the entire engine operational range.
• outputs a command to the fuel injectors to meter the appropriate quantity of fuel.
• determines and compensates for the age of the vehicle and its uniqueness.
• automatically senses and compensates for changes in altitude (for example, from sea level to  mountains).

To maintain the required exhaust emission levels, the fuel delivery system must be:

• kept in good operating condition.
• adjusted to specifications on the Vehicle Emission Control Information (VECI) decal.

The fuel delivery sub-system consists of:

• a high-pressure in-tank mounted fuel pump.
• a fuel filter/reservoir delivering fuel from the fuel tank through a 20-micron fuel filter to a fuel injection  supply manifold
• the fuel injection supply manifold which incorporates electrically-actuated fuel injectors mounted  directly above each of the engine's eight intake ports.
• the fuel injectors which spray a metered quantity of fuel into the intake air stream when energized.

• connected in series with the fuel injectors.
• positioned downstream from fuel injectors.

Fuel Injection Timing

For fuel injection timing:

• Air entering the engine is monitored by flow, pressure and temperature sensors.
• The signals from the electronic engine control sensors are processed by the powertrain control  module (PCM).
• The powertrain control module determines the needed fuel injector pulse width and sends a  command to the fuel injectors  to meter the exact quantity of fuel.
• Each fuel injector is energized once every other crankshaft revolution in sequence with engine firing  order.
• The period of time that the fuel injectors are energized (fuel injector "on time" or pulse width) is  controlled by the vehicle's powertrain control module.

The sequential multiport fuel injection (SFI) system is classified as follows:

• multi-point
• pulse time
• mass air flow controlled

Air Induction System

The air induction system supplies filtered air to the engine to mix with the fuel for combustion purposes and consists of the following:

• air intake resonator
• engine air cleaner (ACL) with air cleaner element (ACL element)
• mass air flow sensor (MAF sensor)
• air cleaner outlet tube
• intake manifold with integral intake manifold runner control (IMRC) assemblies

The throttle body has the following features:

• controls airflow to the engine through a butterfly-type valve.
• throttle position is controlled by a single lever and accelerator cable linkage.
• die-cast aluminum, single-piece body
• a single bore with an intake air channel around the throttle valve. This channel controls both cold and warm intake air control as regulated by an idle air control valve (IAC valve) which is mounted to the surge tank connector.
• a throttle body-mounted throttle position sensor (TP sensor).

The idle air control valve:

• is an electro-mechanical device controlled by the powertrain control module (PCM).
• incorporates a linear actuator which positions a variable area metering valve.

The intake manifold is made up of the:

• intake surge tank.
• LH and RH intake runners.
• LH and RH air horns.

The entire intake manifold system must be removed to allow access to:

•  fuel injectors.
•  fuel injection supply manifold.

• throttle body.
• EGR valve (EGR valve).
• EGR backpressure transducer.
• intake manifold runner controls.

• an intake surge tank
• LH and RH intake runners. The primary runner is always open. A secondary runner is controlled by an electronically operated intake manifold runner control (IMRC) deactivation motor and is open at high engine rpm.
• vacuum taps for EGR valve, fuel pressure regulator, evaporative emission canister purge and power brake booster are provided on the intake surge tank.

The fuel injectors are:

• electro-mechanical devices which meter and atomize fuel delivered to the engine.
• mounted in the lower intake manifold (IMRC) and positioned so that their tips are directing fuel just  before the engine intake valve.

• fuel flow is regulated by the length of time the solenoid is energized.
• fuel is atomized by the director plate at the point where the fuel separates.

Fuel Injection Supply Manifold

The fuel injection supply manifold delivers high-pressure fuel from the vehicle fuel supply line to the fuel injectors. The fuel injection supply manifold consists of:

• mounting flanges for the fuel pressure regulator.
• mounting attachments which locate the fuel injection supply manifold and provide fuel injector  retention.
• fuel inlet and outlet connections with push connect fittings.

Fuel Pressure Regulator

The fuel pressure regulator:

• is attached to the fuel injection supply manifold downstream of the fuel injectors.
• regulates the fuel pressure supplied to the fuel injectors.
• 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.
• nominal fuel pressure is established by a spring preload applied to the diaphragm.
• balances one side of the diaphragm with manifold pressure to maintain a constant fuel pressure  drop across the fuel injectors.
• bypasses and returns excess fuel to the fuel tank.

The fuel pressure relief valve:

• is used to relieve fuel pressure from the fuel system.
• is located on the fuel injection supply manifold.

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.

Fuel Pump Relay

The fuel pump relay:

• is integral to the constant control relay module.
• supplies power to the fuel pump when the powertrain control module (PCM) grounds the relay during  starting and engine running conditions.

The A/C clutch control relay:

• is integral to the constant control relay module.
• cuts off the A/C to improve idle smoothness after engine start-up.
• cuts off the A/C to improve acceleration performance.

The A/C is also cut off when the throttle position sensor (TP sensor) indicates a wide open throttle condition.