The fuel supply system consists of the following components:

The fuel tank, at the rear of the underbody, is held in place by 2 metal straps. Anti-squeak pieces are used on top of the tank to reduce rattles.

In order to help prevent refueling with leaded gasoline, the fuel filler neck on a gasoline engine vehicles has a built-in restrictor and deflector. The opening in the restrictor will only admit the smaller unleaded gas nozzle spout, which must be fully inserted to bypass the deflector.

Attempted refueling with a leaded gas nozzle or failure to fully insert the unleaded gas nozzle results in gasoline splashing back out of the filler neck.

The fuel tank filler neck is equipped with a tethered fuel tank filler cap. Turn the cap counterclockwise in order to remove. A built-in torque-limiting device prevents overtightening. In order to install the cap, turn the cap clockwise until a clicking noise is heard. The clicking is a signal to the operator that the correct torque has been reached and the cap is fully seated.

The fuel balance control system consists of the following components:

On vehicles with dual tanks, the front tank is the main and the rear tank is the auxiliary. The main fuel balance pump supplies fuel to the fuel injection unit. The low pressure (about 32 kPa or 7 psi) fuel balance pump is used only to transfer fuel from the auxiliary tank to the main tank in order to balance the fuel levels in both tanks. As the main tank level drops to about 25% below the level in the auxiliary tank, the fuel sender and balance module energizes the fuel pump relay. This pumps the fuel from the auxiliary tank to the main tank. When the level in the main tank reaches a level slightly higher than the level in the auxiliary tank, or the auxiliary tank is empty, the module de-energizes the balance pump relay and fuel pump. Any malfunction in either of the fuel gage circuits will disable the system and the fuel will not be transferred from the auxiliary fuel tank to the main fuel tank.

The fuel sender assembly is located inside the fuel tank and attaches to the top of the fuel tank.

The fuel sender assembly consists of the following major components:

The fuel pump is a high pressure rollervane type, electric pump, which mounts in the fuel tank. Fuel is pumped, at a specified flow and pressure from the fuel pump, through the in-line filter to the pressure regulator in the fuel injection unit. Excess fuel is returned to the fuel tank through the fuel return line.

The fuel pump attaches to the fuel sender assembly. A fuel strainer attaches to the fuel pump inlet line. The strainer prevents dirt particles from entering the fuel line and tends to separate water from the fuel. A ceramic resistor card for the fuel level sensor is also attached to the outside of the sender assembly. The function of the ceramic resistor card is to vary the resistance, depending on the position of the float and to send a signal to the fuel gage via the BCM. The modular fuel sender assembly is serviced as a complete assembly. The only serviceable components on the modular unit are the strainer, fuel level sensor, and the OBD II fuel tank pressure sensor.

A woven plastic filter attaches to the lower end of the fuel pump in the fuel tank. The functions of the strainer are to filter contaminants and to wick fuel.

The life of the fuel pump strainer is generally considered to be that of the fuel pump. The fuel pump strainer is self-cleaning and normally requires no maintenance. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment or water. In which case the fuel tank should have a thorough cleaning. Refer to Fuel System Cleaning (Purge the Fuel Tank) for V6. Refer to Fuel System Cleaning (Purge the Fuel Tank) for V8. If the fuel strainer is plugged, replace the strainer with a new fuel pump strainer.

A steel in-line fuel filter is used in the fuel feed pipe ahead of the fuel injection system. The filter element is made of paper and is designed to trap particles in the fuel that may cause damage to the injection system. The filter housing is constructed to withstand maximum fuel system pressure, exposure to fuel additives and changes in temperature.

Caution: In order to Reduce the Risk of Fire and Personal Injury:

Nylon fuel pipes are designed to perform the same job as the steel or rubber fuel tubes they replace. Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives and changes in temperature. There are two sizes used: 3/8 in. ID for the fuel feed and 5/16 in. ID for the fuel return.

The fuel feed and return pipes are assembled as a harness. Retaining clips hold the pipes together and provide a means for attaching the pipes to the vehicle. Quick-connect type fittings are used at the fuel tank ends of the fuel feed/return pipes and at the in-line fuel filter. They are described below. Sections of the pipes that are exposed to chafing, high temperature or vibration are protected with a heat resistant rubber hose and/or corrugated plastic conduit.

Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if forced into sharp bends, nylon pipes will kink and restrict fuel flow. Once exposed to fuel, nylon pipes may become stiffer and are more likely to kink if bent too far. Special care should be taken when working on a vehicle with nylon fuel pipes.

Quick-connect type fittings provide a simplified means of installing and connecting the fuel system components. The quick-connect fittings consists of a female socket and a compatible male connector. O-rings, located inside the female socket, provide the fuel seal. Integral locking tabs or fingers hold the fittings together. The metal collar quick-connect fittings have locking tabs that require a special tool to release. Refer to Fuel Hose and Pipes (Quick Connect Fittings) .

Caution: In order to Reduce the Risk of Fire and Personal Injury:

The vapor pipe extends from the fuel sender assembly to the charcoal canister. It is made up of nylon pipe and is connected to the fuel sender assembly and the EVAP canister with the fuel resistant rubber hoses.

The fuel feed and return pipe threaded connections at the fuel injection unit are sealed with replaceable O-ring seals. These O-ring seals are made of special material and should only be serviced with the correct service part.

When the key is turned ON with out the engine running, the control module turns a fuel pump relay ON for two seconds. This builds up fuel pressure quickly. If the engine is not started within two seconds, the control module shuts the fuel pump OFF and waits until the engine starts. As soon as the engine is cranked, the control module turns the relay ON and runs the fuel pump. When the engine is cranking or running, the control module receives the crankshaft position (CKP) sensor reference pulses which in turn energize the fuel injectors. As a backup system to the fuel pump relay, the fuel pump can also be turned ON by a fuel pump oil pressure switch. When the engine reaches about 28 kPa (4 psi), and the fuel pump relay does not complete the circuit, the fuel pump oil pressure switch will close to complete the circuit to run the fuel pump. An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. The fuel pump oil pressure switch will turn ON the fuel pump as soon as oil pressure reaches about 28 kPa (4 psi).

The accelerator control system is a control cable type attached at one end to an accelerator pedal assembly. On the other end is the throttle valve.

Fuel System Overview

The fuel system is controlled by the control module located in the engine compartment. The control module is the control center of the system.

The basic function of the fuel system is to control fuel delivery to the engine under all operating conditions. The following two types of fuel injection systems deliver the fuel to the engine:

The main control sensor is the heated oxygen sensor (HO2S). The HO2S is located in the exhaust manifold. The HO2S tells the control module the amount of oxygen in the exhaust gas. The control module changes the air to fuel ratio to the engine by controlling the fuel injector. Efficient catalytic converter operation requires a 14.7:1 air to fuel ratio. Because the constant measuring and adjusting of the air to fuel ratio, the fuel injection system is called a Closed Loop system.

Several other important engine operation parameters include the following items:

These parameters determine the mode of engine operation.

The following are the 3 separate classifications of fuel systems:

The control module monitors the voltages from several sensors in order to determine how much fuel to give the engine. The fuel is delivered under one of several conditions called modes. The control module controls all of the modes.

When the ignition switch is turned to the ON position, before engaging the starter, the control module energizes the fuel pump relay for 2 seconds allowing the fuel pump to build up pressure. The control module then checks the engine coolant temperature (ECT) sensor and the throttle position (TP) sensor in order to determine the proper air and fuel ratio for starting. The control module controls the amount of fuel delivered in the starting mode by changing how long the injectors are energized. This is done by pulsing the injectors for very short times.

If the engine floods, clear the engine by depressing the accelerator pedal down to the floor. The control module then pulses the injector at a 16.5:1 air to fuel ratio. The control module holds this injector rate as long as the throttle stays wide open and the engine is below 600 RPM. If the throttle position becomes less than 65 percent, the control module returns to the starting mode.

The Run Mode is the mode under which the engine operates most of the time. In this mode, the engine operates in either Open Loop or Closed Loop.

Open Loop

When the engine is first started and it is above 400 RPM, the system goes into the open loop operation. In the open loop, the control module ignores the signal from the HO2S, and the control module calculates the air to fuel ratio based on the inputs from the engine coolant temperature (ECT) sensor and manifold absolute pressure (MAP) sensor.

The system stays in open loop until the following conditions are met:

1. The HO2S has varying voltage output, showing that it is hot enough to operate properly. This depends on engine temperature.
2. The engine coolant temperature (ECT) sensor is above a specified temperature.
3. A specific amount of time has elapsed after starting the engine.

A normal functioning system may go into an open loop at idle if the heated oxygen sensor (HO2S) temperature drops below the minimum requirement to produce the voltage fluctuation.

Closed Loop

The specific values for the above conditions vary with different engines. When these conditions are met, the systems goes into a closed loop operation. In a closed loop, the control module calculates the air to fuel ratio (injector on-time) based on the signal from the HO2S. This allows the air to fuel ratio to stay very close to 14.7:1.

When the control module senses rapid changes in the throttle position and the manifold pressure, the system enters the acceleration mode. The system provides the extra fuel needed for smooth acceleration.

When the driver releases the accelerator pedal, the air flow into the engine is reduced. The corresponding changes in the throttle position and the manifold air pressure are relayed to the control module, which reduces the injector pulse width, in order to reduce the fuel flow. If the decel is very rapid, or for long periods (such as long closed throttle coast-down), the control module shuts OFF the fuel completely in order to protect the catalytic converter.

In order to prevent possible engine damage from over-speed, the control module cuts off fuel from the fuel injectors when the engine speed is above approximately 5,500 RPM with the vehicle in any forward gear or reverse. In order to prevent tire damage, the control module also has a fuel cutoff in excess of 108 mph (173 km/h) based on the speed rating of the tires.

Fuel is also cutoff during rapid deceleration. See Deceleration Mode.

The control module constantly monitors engine operation and estimates the conditions that could result in high converter temperatures. If the control module determines the converter may overheat, this causes the system to return to the Open Loop operation and enriches the fuel mixture.

When battery voltage is low, the control module can compensate for a weak spark delivered to the distributor by increasing the following items: