Fuel Return Line: Description and Operation

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 filter back to the fuel tank. The fuel pipes consist of 3 sections:
- The rear fuel pipe assemblies are located from the top of the fuel tank to the fuel filter. The rear fuel pipes are constructed of nylon.
- The chassis fuel pipe is located under the vehicle and connects the rear fuel pipes to the engine compartment fuel pipe. The chassis fuel pipe is constructed of steel with a section of rubber hose.
- The engine compartment fuel pipe connects the chassis fuel feed pipe to the fuel rail. The engine compartment fuel pipe is constructed of steel.

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 pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. The following 3 sizes of nylon pipes are used:
- 9.53 mm (3/8 in) ID for the fuel feed
- 7.94 mm (5/16 in) ID for the fuel return
- 12.7 mm (1/2 in) 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.