System Overview
The fuel tank stores the fuel supply. An electric fuel pump, located in the fuel tank within the modular fuel sender assembly, pumps fuel through an in-line fuel filter to the fuel rail assembly. The pump provides fuel pressure greater than is needed by the injectors. The fuel pressure regulator keeps fuel available to the injectors at a regulated pressure. A separate fuel pipe is used to return fuel to the fuel tank.
Fuel Tank Vent Valve
The fuel tank vent valve is located in the rear of the vehicle near the fuel tank. The fuel tank vent valve is a pressure/vacuum relief valve. When the fuel tank pressure exceeds a specified pressure, the valve opens allowing the tank pressure to bleed off. When the fuel tank is in a vacuum condition, the vent valve opens when the vacuum is within a specified range allowing fresh air to be pulled in.
Fuel Tank
The fuel tank stores the fuel supply. The fuel tank is located in the rear of the vehicle. The fuel tank is held in place by two metal straps that attach to the frame. The fuel tank is made of steel and is coated internally with a special corrosion inhibitor.
Fuel Tank Filler Pipe
The fuel tank filler pipe has a built-in restrictor and deflector in order to prevent refueling with leaded fuel.
Fuel Filler Cap
Notice: If a fuel tank filler cap requires replacement, use only a fuel tank filler cap with the same features. Failure to use the correct fuel tank filler cap can result in a serious malfunction of the fuel and EVAP system.
The fuel tank filler neck is equipped with a tethered fuel filler cap. The cap requires a quarter of a turn to remove it. A built in torque-limiting device prevents over tightening. In order to install the cap, turn the cap clockwise until you hear three audible clicks. This signals that the correct torque has been reached and the cap is fully seated. A fuel filler cap that is not fully seated may cause a malfunction in the emission system.
Modular Fuel Sender Assembly
The Modular Fuel Sender Assembly consists of the following major components: fuel sender strainer, fuel pump strainer, roll-over valve, fuel level sensor, and fuel tank pressure sensor.
Fuel Level Sensor
The Fuel Level Sensor consists of the following components: float, the wire float arm, and the ceramic resistor card. The Fuel Level Sensor is mounted on the Modular Fuel Sender Assembly and is used as an input to the PCM. The PCM uses this information as a fuel level input for Various diagnostics. In addition the PCM transmits the fuel level over the Class ll communication circuit to the IP cluster. This information is used for the IP Fuel Gauge, and low Fuel Warning indicator if applicable.
Fuel Pump
The fuel pump is mounted in the fuel reservoir within the modular fuel sender. The fuel pump is an electric high pressure gerotor pump. The fuel is pumped to the fuel rail at a specified flow and pressure. Excess fuel returns to the fuel tank by a return pipe. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The electric fuel pump operation is controlled by the Powertrain Control Module (PCM) through a fuel pump relay. The fuel pump flex pipe acts to dampen the fuel pulses and noise generated by the fuel pump. The fuel pump is serviced as part of the Modular Fuel Sender.
Fuel Pressure Regulator Assembly
The fuel pressure regulator attaches to the fuel rail on the fuel return side. The fuel pressure is a diaphragm operated relief valve and is referenced to manifold vacuum. If the fuel pressure is too low, poor performance could result. If the pressure is to high, excessive odor and a Diagnostic Trouble Code (DTC) may result.
Fuel Pump Strainer
The fuel pump strainer attaches to the lower end of the modular fuel sender assembly. The fuel pump strainer is made of woven plastic. The functions of the fuel pump strainer is to filter contaminants and to wick fuel. The life of the fuel pump strainer is generally considered to be that of the fuel pump, 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 tank should be thoroughly cleaned and replace the plugged fuel pump strainer with a new one.
In-Pipe Fuel Filter
The fuel feed pipe has a steel fuel filter installed ahead of the fuel injection system. The paper filter element (2) traps particles in the fuel that may damage the injection system. The filter housing (1) is made to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. The fuel filter has a quick-connect inlet fitting and a threaded outlet fitting. The threaded fitting is sealed with an O-ring. There is no service interval for fuel filter replacement. Replace a restricted fuel filter.
Fuel Feed and Fuel Return Pipes
The fuel feed and fuel return pipes carry fuel from the modular fuel sender assembly to the fuel injection system and back to the modular fuel sender assembly.
Fuel Tank Vapor Pressure Sensor
The fuel tank pressure sensor is used to detect small leaks in the evaporative emission system. The fuel tank pressure sensor is a three wire strain gauge sensor much like that of the common GM MAP sensor. However, this sensor has very different electrical characteristics due to its pressure differential design. The sensor measures the difference between the air pressure (or vacuum) in the fuel tank and the outside air pressure. The sensor mounts at the top of the fuel tank. A three wire electrical harness connects it to the Powertrain Control Module (PCM). The PCM supplies a five volt reference voltage and ground to the sensor. The sensor will return a voltage between 0.1 and 4.9 volts. When the air pressure in the fuel tank is equal to the outside air pressure, such as when the fuel fill cap is removed, the output voltage of the sensor will be 1.3 to 1.7 volts.
Fuel Feed and Return Pipes
The fuel feed pipe carries fuel from the fuel tank to the fuel rail assembly. The fuel return pipe carries fuel from the fuel rail assembly back to the fuel tank. The fuel feed and return pipes consist of three sections:
| • | The rear fuel pipe assemblies are located from the top of the fuel tank to the chassis fuel pipes. The rear fuel pipes are constructed of nylon. |
| • | The chassis fuel pipes are located under the vehicle and connect the rear fuel pipes to the engine compartment connecting fuel pipes. These pipes are constructed of steel. |
| • | The engine compartment connecting fuel pipes connect the chassis pipes to the engine fuel rail. These fuel pipes are constructed of nylon. |
Nylon Fuel Pipes
Caution: In order to reduce the risk of fire and personal injury observe the
following items:
• Replace all nylon fuel pipes that are nicked, scratched or damaged
during installation, do not attempt to repair the sections of the nylon fuel
pipes • Do not hammer directly on the fuel harness body clips when installing
new fuel pipes. Damage to the nylon pipes may result in a fuel leak. • Always cover nylon vapor pipes with a wet towel before using a
torch near them. Also, never expose the vehicle to temperatures higher than
115°C (239°F) for more than one hour, or more than 90°C (194°F)
for any extended period. • Apply a few drops of clean engine oil to the male pipe ends before
connecting fuel pipe fittings. This will ensure proper reconnection and prevent
a possible fuel leak. (During normal operation, the O-rings located in the
female connector will swell and may prevent proper reconnection if not lubricated.)
Nylon fuel pipes are designed to perform the same job as the steel or flexible fuel pipes or hoses that they replace. Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There are three sizes of nylon fuel pipes used: 3/8 in ID for the fuel feed, 5/16 in ID for the fuel return, and 1/2 in ID for the vent.
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. Heat resistant rubber hose and/or corrugated plastic conduit protect the sections of the pipes that are exposed to chafing, high temperature or vibration.
Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if nylon fuel pipes are forced into sharp bends, the pipes will kink and restrict the fuel flow. Also, once exposed to fuel, nylon pipes may become stiffer and are more likely to kink if bent too far. Take special care when working on a vehicle with nylon fuel pipes.
Quick-Connect Fittings
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.
Fuel Pipe O-Rings
An O-ring seals the threaded connection at the fuel filter. Fuel system O-ring seals are made of special material. Service the O-ring seals with the correct service part.
Fuel Tank Pressure Sensor
The Fuel Tank Pressure (FTP) Sensor measures the difference between the air pressure (or vacuum) in the fuel tank and the outside air pressure.
The sensor mounts at the top of the fuel tank sending unit. The PCM supplies a 5 volt reference voltage and ground to the sensor. The sensor provides a signal voltage between 0.1-4.9 volts to the PCM. When the air pressure in the fuel tank is equal to the outside air pressure, such as when the fuel fill cap is removed, the output voltage of the sensor will measure 1.3-1.7 volts.
When the air pressure in the tank is 4.5 inches H2O (1.25 kPa), the sensor output voltage should measure 0.5 ± 0.2 volts (1.25 kPa).
The sensor voltage increases to approximately 4.5 volts at 14 inches of H2O (-3.75 kPa).
