The modular fuel sender assembly mounts to the threaded opening of the plastic fuel tank with a seal and a retainer ring. The reservoir, containing the exterior inlet strainer, the electric fuel pump and the pump strainer, maintains contact with the tank bottom. This design provides:

The modular fuel sender assembly maintains an optimum fuel level in the reservoir (bucket). The fuel entering the reservoir is drawn in by the following components:

The electric fuel pump is a turbine pump which is located inside of the modular fuel sender. The electric fuel pump operation is controlled by the engine control module (ECM) through the fuel pump relay.

The fuel pressure regulator is a diaphragm-operated relief valve located in the modular fuel pump and sender assembly. Its principal function is to maintain a controlled pressure at the injectors at all times by regulating fuel flow into the fuel feed line. With the ignition ON and the engine OFF, system fuel pressure at the pressure test connection should be 380-440 kPa (55-64 psi).

The strainers act as a coarse filter to perform the following functions:

Fuel stoppage at the strainer indicates that the fuel tank contains an abnormal amount of sediment or water. Therefore, the fuel tank will need to be removed and cleaned, and the filter strainer should be replaced.

The fuel filter assembly is contained within the modular fuel pump and sender assembly reservoir and forms the containment housing for the fuel pump. The filter comprises a paper element which traps particles in the fuel that may damage the fuel injection system. The fuel filter is made to withstand maximum fuel system pressure, changes in temperature and exposure to fuel additives.

The fuel level sender assembly comprises of two fuel level float and wire arm assemblies, a ceramic variable resistor card assembly , and a detachable nylon wiper. The ceramic resistor card is attached to a plastic card holder which attaches to the reservoir. A metal contact fork with brushes is connected to the detachable nylon wiper. This assembly provides a variable circuit resistance to the engine control module (ECM) depending on wiper contact position. Two circuit wires run from the resistor card and extend up to connect with the modular fuel pump to cover assembly wiring connector on the underside of the modular fuel pump and sender assembly cover. The ECM averages out any slosh variation in the fuel tank and sends this signal to the fuel level indicator on the instrument panel fuel gauge.

Quick-connect fittings provide a simplified means of installing and connecting fuel system components. The fittings consist of a unique female connector and a compatible male pipe end. "O" rings, located inside the female connector, provide the fuel seal. Integral locking tabs or fingers hold the fittings together.

"O" rings seal the threaded connections in the fuel system. The fuel system "O" ring seals are made of a special material. The fuel pipe "O" rings are not a serviceable item.

The evaporative emission (EVAP) tubes extend from the fuel tank module and the EVAP canister vent to the EVAP canister. These tubes are located on the top rear of the fuel tank. The EVAP purge tube/pipe extends from the EVAP canister on top of the fuel tank to the EVAP purge solenoid in the engine compartment. The chassis EVAP purge pipe is constructed of steel.

The fuel rail consists of 3 parts:

The fuel rail is mounted on the intake manifold and distributes the fuel to each cylinder through the individual injectors.

The fuel injector is a solenoid device that is controlled by the ECM. When the ECM energizes the injector coil, a normally closed ball valve opens, allowing the fuel to flow past a director plate to the injector outlet. The director plate has holes that control the fuel flow, generating a dual conical spray pattern of finely atomized fuel at the injector outlet. The fuel from the outlet is directed at both of the intake valves, causing the fuel to become further vaporized before entering the combustion chamber.

The fuel injectors will cause various driveability conditions if the following conditions occur:

When the ignition switch is in the ON position, before engaging the starter, the engine control module (ECM) energizes the fuel pump relay for two seconds, causing the fuel pump to pressurize the fuel system. If the ECM does not receive ignition reference pulses with the engine cranking or running within two seconds, the ECM shuts OFF the fuel pump relay, causing the fuel pump to stop.

The engine is fuelled by six individual injectors, one for each cylinder, that are controlled by the ECM. The ECM controls each injector by energizing the injector coil for a brief period once every other engine revolution. The length of this brief period, or pulse, is carefully calculated by the ECM to deliver the correct amount of fuel for proper driveability and emissions control. The period of time when the injector is energized is called the pulse width and is measured in milliseconds, thousandths of a second.

While the engine is running, the ECM is constantly monitoring the inputs and recalculating the appropriate pulse width for each injector. The pulse width calculation is based on the injector flow rate, mass of fuel the energized injector will pass per unit of time, the desired air/fuel ratio, and actual air mass in each cylinder and is adjusted for battery voltage, short term, and long term fuel trim. The calculated pulse is timed to occur as each cylinders intake valves are closing to attain largest duration and most vaporization.

Fuelling during a crank is slightly different than fuelling during an engine run. As the engine begins to turn, a prime pulse may be injected to speed starting. As soon as the ECM can determine where in the firing order the engine is, the ECM begins pulsing the injectors. The pulse width during the crank is based on the coolant temperature and the engine load.

The Fuelling system has several automatic adjustments in order to compensate for the differences in the fuel system hardware, the driving conditions, the fuel used, and the vehicle aging. The basis for the fuel control is the pulse width calculation that is described above. Included in this calculation are an adjustment for the battery voltage, the short term fuel trim, and the long term fuel trim. The battery voltage adjustment is necessary since the changes in the voltage across the injector affect the injector flow rate. The short term and the long term fuel trims are fine and gross adjustments to the pulse width that are designed in order to maximize the driveability and emissions control. These fuel trims are based on the feedback from the oxygen sensors in the exhaust stream and are only used when the fuel control system is in a Closed Loop operation.

Under certain conditions, the Fuelling system will turn OFF the injectors for a period of time. This is referred to as fuel shut-off. Fuel shut-off is used in order to improve traction, save fuel, improve emissions, and protect the vehicle under certain extreme or abusive conditions.

In case of a major internal failure, the ECM may be able to use a back-up fuel strategy for limp in mode that will run the engine until service can be performed.

The ECM controls the fuel injectors based on information that the ECM receives from several information sensors. Each injector is fired individually in the engine firing order, which is called sequential fuel injection. This allows precise fuel metering to each cylinder and improves the driveability under all of the driving conditions.

The ECM has several operating modes for fuel control, depending on the information that has been received from the sensors.

With the ignition ON, before engaging the starter, the engine control module (ECM) energizes the fuel pump relay for two seconds allowing the fuel pump to build up pressure. The ECM first checks speed density, then switches to the mass air flow (MAF) sensor. The ECM also uses the engine coolant temperature (ECT), throttle position (TP), and manifold absolute pressure (MAP) sensors to determine the proper air/fuel ratio for starting. The ECM controls the amount of fuel delivered in the starting mode by changing the pulse width of the injectors. This is done by pulsing the injectors for very short times.

If the engine is flooded with fuel during starting and will not start, the Clear Flood Mode can be manually selected. To select Clear Flood Mode, push the accelerator to wide open throttle (WOT). With this signal, the ECM will completely turn OFF the injectors and will maintain this stage as long as the ECM indicates a WOT condition with engine speed below 1,000 RPM.

The Run Mode has 2 conditions: Open Loop operation and Closed Loop operation. When the engine is first started and the engine speed is above 480 RPM, the system goes into Open Loop operation. In Open Loop operation, the ECM ignores the signals from the oxygen sensors and calculates the required injector pulse width based primarily on inputs from the MAF, IAT and ECT sensors.

In Closed Loop, the ECM adjusts the calculated injector pulse width for each bank of injectors based on the signals from each oxygen sensor.

The ECM monitors the changes in the TP and the MAF sensor signals in order to determine when the vehicle is being accelerated. The ECM will then increase the injector pulse width in order to provide more fuel for enhanced performance.

The ECM monitors changes in TP and MAF sensor signals to determine when the vehicle is being decelerated. The ECM will then decrease injector pulse width or even shut OFF injectors for short periods to reduce exhaust emissions, and for better (engine braking) deceleration.

The ECM can compensate in order to maintain acceptable vehicle driveability when the ECM sees a low battery voltage condition. The ECM compensates by performing the following functions:

The engine control module (ECM) cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability:

The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. The ECM monitors the heated oxygen sensor (HO2S) signal voltage while in Closed Loop and regulates the fuel delivery by adjusting the pulse width of the fuel injectors based on this signal. The ideal fuel trim values are around 0 percent for both short term and long term fuel trim. A positive fuel trim value indicates the ECM is adding fuel in order to compensate for a lean condition by increasing the pulse width. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition by decreasing the pulse width. A change made to the fuel delivery changes the short term and long term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltage. These changes fine tune the engine fuelling. The long term fuel trim makes coarse adjustments to the fuelling in order to re-centre and restore control to short term fuel trim. A scan tool can be used to monitor the short term and long term fuel trim values. The long term fuel trim diagnostic is based on an average of several of the long term speed load learn cells. The ECM selects the cells based on the engine speed and engine load. If the ECM detects an lean or rich condition, the ECM will set a fuel trim DTC.