GM 6.5L V8 – Fuel System – Fuel Tank Assembly

On some vehicles, the fuel tank assembly mounts on the left framerail (see Figure 7-2, view A). Other vehicles have a fuel tank mounted behind the rear axle assembly that is supported between the left and right framerails (see Figure 7-2, view B). In either case, the fuel tank has a filler tube with a flexible coupling and screw-type clamps.

The fuel tank has a removeable pick-up/sending unit (see Figure 7-3). The pick-up tube has a saran filter sock with a bypass valve that opens when the filter becomes excessively restricted. The sending unit is a variable resistor with a wiper contact moved by a float.
The pick-up/sending unit has threaded fittings with O-ring seals for the fuel supply and return hoses. The sealing of these fittings is critical to the correct operation of the fuel system. Loose parts can allow air to enter the fuel supply system, affecting the operation of the fuel injection pump.

The fuel tank supplies the lift pump with fuel under a low (suction) pressure (see Figure 7-4). Fuel used to cool and lubricate the injection pump and eight nozzles returns to the fuel tank under a low pressure.
The filler cap of the fuel tank has a two-way check valve that limits fuel tank pressure to 2 psi and vacuum to 1 inch Hg. Correct fuel tank pressure is critical to the operation of the entire fuel system.


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