GM 6.5L V8 – Fuel System – Fuel Filter Assembly


The fuel filter assembly mounts on the rear of the intake manifold, using two bolts (see Figure 7-10, view A). The filter housing has an inlet fitting connecting to the pipe/hose from the lift pump and an outlet fitting connecting to the fuel injection pump with a hose. A third fitting connects through a hose to a drain valve mounted on the water crossover/thermostat (see Figure 7-10, view B).
The fuel filter assembly has a two-stage replaceable element with integral seals (refer to Figure 7-9). A threaded nut retains the element in the housing. The element has an air vent valve on its top surface that is used during a filter element replacement procedure.

The fuel filter assembly has a fuel heater mounted to its bottom side that is retained with a threaded nut and seal ring (refer to Figure 7-12). Another part of the fuel filter assembly is a Water In Fuel (WIF) sensor. The WIF sensor has an O-ring seal and two mounting screws. Three wires connect the WIF sensor to a power supply circuit, as well as to an instrument cluster-mounted amber warning lamp.
Figure 7-13 shows a section view of the fuel filter assembly.


The fuel filter element separates particles larger than 10 microns (0.00039-in.) from fuel moving through it under lift pump pressure (see Figure 7-14 ). Filter action is very critical to the operation of internal parts of the fuel injection pump, such as the transfer pump, rotor and automatic advance mechanism.
The path of fuel under lift pump pressure inside the fuel filter assembly is as follows (refer to Figure 7-15):
• From the inlet fitting into the bottom of the housing
• Past the fuel heater element to the primary stage of the filter element
• Through the primary filter element (from the inside to the outside) to the secondary filter element
• Through the secondary filter element (from the outside to the inside) to the screen
• Through the screen to the outlet fitting
• From the fuel filter outlet fitting to the transfer pump inside the fuel injection pump
The 6.5L V8 turbo diesel engine does not use a sensor to detect excessive filter element restriction, and no instrument cluster-mounted CHANGE FILTER lamp exists.

Figure 7-16 shows the flow of fuel into and out of the fuel filter, as well as from the transfer pump inside the fuel injection pump to various components. The pressure, volume and quality of the fuel exiting the fuel filter has a major effect on the performance of the injection pump.

The design of the filter element includes a coalescent area that allows water droplets (as small as one micron) to separate from the fuel and collect in a lower portion of the housing (see Figure 7-17). The WIF sensor has a capacitive probe controlled by an electronic ciruit inside the sensor that allows it to detect a certain amount of water in the fuel inside the filter housing and then complete the SERVICE FUEL FILTER warning lamp circuit in the instrument cluster to alert the driver. The vehicle owner’s manual directs the driver to drain the filter when this condition occurs.
When the ignition switch is first turned to the RUN position, the WIF sensor will complete the SERVICE FUEL FILTER lamp circuit for 2 to 5 seconds. This action provides a bulb check for the vehicle driver.
See page 8-35 for information about the WIF sensor electrical circuit.

The heater portion of the fuel filter assembly operates when the temperature of fuel at the inlet of the filter housing is cold enough to possibly cause waxing that could restrict flow to the injection pump (see Figure 7-18). A control circuit inside the fuel heater completes the circuit for the heater element when it senses a temperature below 46° F (8° C).
See page 8-34 for more information about the fuel heater circuit.


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