For 1990-2009 cars

### Fuel System Overview

This vehicle is equipped with a returnless fuel system. The fuel pressure regulator is a part of the modular fuel sender assembly, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the modular fuel sender assembly inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system.

### Fuel Filler Cap

Notice: Use a fuel tank filler pipe cap with the same features as the original when a replacement is necessary. Failure to use the correct fuel tank filler pipe cap can result in a serious malfunction of the fuel system.

The fuel tank filler pipe is equipped with a turn to vent screw on the type cap which incorporates a ratchet action in order to prevent over-tightening.

The turn to vent feature allows the fuel tank pressure relief prior to removal. Instructions for proper use are imprinted on the cap cover. A vacuum safety relief valve is incorporated into this cap.

### Fuel Pump

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.

### Fuel Sender Strainers

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

• | Filter contaminants

• | Separate water from fuel

• | Provide a wicking action that helps draw fuel into the fuel pump

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

### In-Line Fuel Filter

The fuel filter is located on the fuel feed pipe, between the fuel pump and the fuel rail. The electric fuel pump supplies fuel through the in-line fuel filter to the fuel injection system. The fuel pressure regulator keeps the fuel available to the fuel injectors at a regulated pressure. The fuel filter paper element traps particles in the fuel that may damage the fuel injection system. The fuel filter housing is made to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There is no service interval for fuel filter replacement.

### Fuel Pressure Regulator

The fuel pressure regulator attaches to the fuel return pipe on the modular fuel sender assembly. The fuel pressure regulator is a diaphragm-operated relief valve. A software bias compensates the injector on-time because the fuel pressure regulator is not referenced to manifold vacuum. The injector pulse width varies with the signal from the manifold absolute pressure (MAP)/intake air temperature (IAT) sensors.

### On-Board Refueling Vapor Recovery (ORVR) System (If Equipped)

The on-board refueling vapor recovery (ORVR) system is an on-board vehicle system to recover fuel vapors during the vehicle refueling operation. The flow of liquid fuel down to the fuel tank filler neck provides a liquid seal. The purpose of ORVR is to prevent refueling vapor from exiting the fuel tank filler neck. The ORVR components are listed below, with a brief description of their operation:

• | The fuel tank--The fuel tank contains the modular fuel sender, the fuel limiter vent valve (FLVV), and 1 rollover valve.

• | The check valve--The check valve limits fuel spit-back from the fuel tank during the refueling operation by allowing fuel flow only into the fuel tank. The check valve is located at the bottom of the fuel filler pipe.

• | The FLVV--The FLVV acts as a shut-off valve. The FLVV is located in the fuel tank. This valve has the following functions:

- | Controlling the fuel tank fill level by closing the primary vent from he fuel tank

- | Preventing fuel from exiting the fuel tank via the vapor line to the canister

- | Providing fuel spillage protection in the event of a vehicle rollover by closing the vapor path from the tank to the engine

### Modular Fuel Sender

#### Fuel System Diagram

(1) | Secondary Fuel Level Sensor - Left
(2) | Fuel Return Pipe from Engine
(3) | Fuel Feed Pipe to Engine
(4) | 2-Way Check Valve - Fuel Supply
(5) | Siphon Jet Pump
(6) | Primary Fuel Level Sensor - Right
(7) | Fuel Reservoir/Bucket
(8) | Fuel Pump
(9) | Fuel Strainer/Pick up
(10) | Return Fuel Check Valve for Reservoir
(11) | Return Fuel Jet Pump
(12) | Fuel Pressure Regulator
(13) | Fuel Transfer Line
(14) | Fuel Strainer/Pickup

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:

• | Optimum fuel level in the integral fuel reservoir during all fuel tank levels and during driving conditions

• | An improved tank fuel level measuring accuracy

• | An improved coarse straining and added pump inlet filtering

• | More extensive internal fuel pump isolation for noiseless operation

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 first stage of the fuel pump through the external strainer

| and/or

• | The secondary umbrella valve

| or

• | The return fuel line, whenever the level of fuel is below the top of the reservoir

### Fuel Injectors

The fuel injectors are pulse width modulated (PWM) solenoids controlled by the engine control module (ECM). The ECM turns ON the fuel injectors in order to open a normally closed ball or pintle valve. This allows fuel to flow into the top of the fuel injectors, past the ball or pintle valve, and through a recessed flow director plate at the injector outlet. The fuel rail is mounted on the intake manifold and distributes the fuel to each cylinder through the individual fuel injectors. The fuel rail consists of 3 parts:

• | The pipe that carries fuel to each injector

• | The fuel pressure test port (If Equipped)

• | Iindividual fuel injectors

The director plate has machined holes that control the fuel flow, generating a conical spray pattern of finely atomized fuel at the fuel injector tip. Fuel from the tip is directed at the intake valve, causing it to become further atomized and vaporized before entering the combustion chamber.

A fuel injector which is partially stuck open may cause the following symptoms:

• | Loss of fuel pressure with ignition OFF

• | Extended crank time

• | Dieseling

### Modes of Operation

Engine Fueling: The engine is fueled by individual fuel injectors, one for each cylinder, that are controlled by the engine control module (ECM). The ECM controls each injector by turning ON the injector coil for a brief period once every other engine revolution. The period of time when the injector is turned ON is called the pulse width and is measured in milliseconds. The pulse width is calculated by the ECM to deliver the correct amount of fuel for proper driveability and emissions control.

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

Fueling during a crank is slightly different than fueling 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 fueling system has several automatic adjustments in order to compensate for the differences in fuel system hardware, driving conditions, fuel used, and vehicle aging. The battery voltage adjustment is necessary since the changes in the voltage across the fuel injector affect the flow rate. The short term and the long term fuel trims are fine and gross adjustments to the pulse width that are designed to maximize 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 Closed Loop operation.

Under certain conditions, the fueling system will turn OFF the injectors for a period of time. This is referred to as fuel cut-off. Fuel cut-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 problem, 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.

Starting Mode: When the engine control module (ECM) detects reference pulses from the crankshaft position (CKP) sensor, the ECM will enable the fuel pump. The fuel pump runs and builds up pressure in the fuel system. The ECM then monitors the manifold absolute pressure (MAP), intake air temperature (IAT), engine coolant temperature (ECT), and the throttle position (TP) sensor signals in order to determine the required injector pulse width for starting.
Clear Flood Mode: If the engine is flooded with fuel during starting and will not start, the Clear Flood Mode can be manually enabled. To enable Clear Flood Mode, press the accelerator to wide open throttle (WOT). The engine control module (ECM) will completely turn OFF the fuel injectors and will maintain this mode as long as the ECM detects a WOT condition with engine speed below a predetermined value.
Run Mode: The Run Mode has 2 conditions called Open Loop operation and Closed Loop operation.
Open Loop: Upon initial engine start up and when the engine speed is more than a predetermined value, the engine control module (ECM) operates the fuel system in Open Loop operation. During Open Loop operation, the ECM ignores the signals from the oxygen sensors and calculates the required fuel injector pulse width based primarily on inputs from the manifold absolute pressure (MAP), intake air temperature (IAT) and engine coolant temperature (ECT) sensors. The ECM operates in open loop until the following conditions are met:

• | The oxygen sensor has a varying output voltage, which indicates it is hot enough to operate properly.

• | The ECT sensor is above a specified temperature.

• | A specific amount of time has elapsed after start up.

Closed Loop: During Closed Loop operation, the fuel injector pulse width is based on the oxygen sensor signal. The ECM uses the oxygen sensor signal to keep the air/fuel ratio close to 14.7:1 as possible.
Acceleration Mode: The engine control module (ECM) monitors the changes in the throttle position (TP) and the manifold absolute pressure (MAP) 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 improved performance.
Deceleration Mode: The engine control module (ECM) monitors changes in throttle position (TP) and manifold absolute pressure (MAP) sensor signals to determine when the vehicle is being decelerated. The ECM will then decrease injector pulse width or even turn OFF injectors for short periods to reduce exhaust emissions, and for better (engine braking) deceleration.
Battery Voltage Correction Mode: 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:

• | Increasing the injector pulse width in order to maintain the proper amount of fuel being delivered

• | Increasing the idle speed to increase the generator output

Fuel Cut-Off Mode: To prevent dieseling or engine run-on, no fuel is delivered to the fuel injectors when the ignition is OFF. To prevent flooding, no fuel is delivered to the fuel injectors when no reference pulses are received from the crankshaft position (CKP) sensor.