Fuel Return Line: Description and Operation

Fig. 16 Fuel Drain Manifold Passage:

The fuel drain manifold is a rifled passage within the cylinder head (Fig. 16). The fuel drain manifold (line) connects to a "T" fitting on the fuel return line. The "T" fitting is located at the rear of the cylinder head.

When the engine is running, and during injection, a small amount of fuel flows past the injector nozzle and is not injected into the combustion chamber. This fuel is used to lubricate the fuel injectors. Excess fuel drains into the fuel drain manifold (or passage). Fuel is drained from this passage into a line at the rear of the cylinder head (Fig. 16). After exiting the cylinder head, fuel is routed (returned) back to the fuel tank. A "T" is installed into the fuel return line (Fig. 16). This "T" is used to allow excess fuel from the injection pump to be returned into the fuel tank. A one-way check valve within the overflow valve prevents fuel (from the fuel drain manifold) from entering the fuel injection pump.

A small amount of fuel is returned from the fuel injectors, while a large amount (about 70% of supplied fuel) is returned from the fuel injection pump.