The fuel system consists of the following component:
The positive displacement gear-type fuel pump is shown in the following illustration. See Figure 25422 .
Positive Displacement Gear Type Fuel Pump
The fuel pump transfers fuel from the supply tank to the Electronic Unit Pumps (EUP). The pump circulates excess fuel supply through the EUPs. This purges the air from the system and cools the EUPs. The unused fuel returns to the fuel tank via the fuel return line.
The fuel pump is directly mounted to the cylinder block.
The small relief valve vent permits the fuel oil in the inlet side of the pump to lubricate the relief valve at its outer end. This eliminates the possibility of a hydrostatic lock. Pressurized fuel contacts the relief valve through the passage to head of the relief valve and provides for relief of excess discharge pressures. Fuel re-enters the inlet side of the pump through the passage to head of the relief valve when the discharge pressure is great enough to move the relief valve back from its seat. Part of the relief valve may be seen through the passage to head of the relief valve. The gear teeth vent cavity provides escape for the fuel oil that is squeezed out of the gear teeth as they mesh on the discharge side of the pump. Otherwise, fuel trapped at the root of the teeth would tend to force the gears apart, resulting in undue wear on the gears, shafts, body, and cover.
Repair of fuel pump is not permissible. Remove and replace faulty fuel pump. See Figure 25355 .
Flowchart for Replacement of Fuel Pump
To remove the fuel pump, perform the following steps: