Circuit - Fuel Drain

The Fuel Drain Circuit incorporates several sources of fuel return. Fuel travels from the fuel tank (via the fuel transfer pump) and is forced through the fuel filter. This fuel then travels into the fuel injection pump. It then goes to a fuel drain line and returns back to the fuel tank.

The fuel that flows to the fuel pump is pressurized by a gear pump and internally transferred to the fuel injection pump. At this point the fuel is channeled into two passages. One passage sends fuel to the FCA (Fuel Control Actuator). The other passage sends fuel to the cascade overflow valve. The overflow valve sends some fuel to a lubrication passage. The rest of the fuel is sent to a drain passage which connects to an external fuel line.

Fuel that travels through the FCA is pressurized by the fuel injection pump and sent through an external high pressure fuel line to the fuel rail. At the fuel rail, fuel is sent to the fuel injectors. If fuel pressure in the fuel rail becomes excessive, the pressure limiting valve opens and sends fuel through an external fuel line.

At the fuel injector, fuel that is not injected is used for lubrication of the fuel injectors. This fuel then travels through an internal passage that is connected to the rear of the cylinder head, an then into an external fuel line. This line is connected to the vehicles fuel return line, and returns excess fuel back into the fuel tank.