Fuel Sender Assembly

The fuel sender assembly is mounted inside the fuel tank. See Figure . The fuel sender assembly consists of the following:

1. Fuel Level Sensor  - See FUEL LEVEL SENSOR  under INPUT DEVICES.
2. Fuel Tank Pressure Sensor  - The Fuel Tank Pressure (FTP) sensor measures the difference between the pressure or vacuum in the fuel tank and outside air pressure. See Fig 1 . The sensor mounts at the top of the fuel tank sending unit. The Powertrain Control Module (PCM) provides a 5-volt reference and a ground to the FTP sensor. The FTP sensor provides a signal voltage back to the control module that can vary between 0.1-4.9 volts. As FTP increases, FTP sensor voltage decreases, high pressure = low voltage. As FTP decreases, FTP voltage increases, low pressure or vacuum = high voltage.

   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 in. H2O (1.12 kPa), the sensor output voltage should measure 0.3- 0.7 volt (1.25 kPa). The sensor voltage increases to approximately 4.5 volts at -14 in. H2O (-3.75 kPa).

   Fig 1: Identifying Fuel Tank Pressure Sensor

   Courtesy of GENERAL MOTORS CORP.
3. Fuel Pump  - See FUEL PUMP  .
4. Fuel Strainer  - The fuel strainer attaches to the lower end of the fuel sender. The fuel strainer is made of woven plastic. See Fig 2 . The functions of the fuel strainer are to filter contaminants and to wick fuel. The fuel strainer normally requires no maintenance. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment or contamination.
   Fig 2: Identifying Fuel Strainer

   Courtesy of GENERAL MOTORS CORP.
5. Fuel Filter  - The fuel filter is located on the fuel feed pipe, between the fuel pump and the fuel injectors. The paper filter element traps particles in the fuel that may damage the fuel injection system. See Fig 3 . The filter housing is made to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature.
   Fig 3: Identifying Fuel Filter

   Courtesy of GENERAL MOTORS CORP.
6. Fuel Feed and Return Pipes  - The fuel feed pipe carries fuel from the fuel tank to the fuel injection system. The fuel return pipe carries fuel from the fuel injection system back to the fuel tank. The fuel pipes consist of 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. Also, chassis fuel pipes are located under the vehicle and connect the rear fuel pipes to the fuel injection system. The chassis fuel pipes are constructed of steel.
7. Nylon Fuel Pipes  - Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There are 3 sizes of nylon pipes used:
   • 3/8" (9.53 mm) ID for the fuel feed.
   • 5/16" (7.94 mm) ID for the fuel return.
   • 1/2" (12.7 mm) ID for the vent.

   Heat resistant rubber hose 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 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.