3516B and 3516B HD Engines and 994D, 994F, and 994H Wheel Loaders Caterpillar

The fuel supply circuit is a conventional design for engines that use fuel injectors. The fuel supply circuit uses a fuel transfer pump to deliver fuel from the fuel tank to the electronic fuel injectors. The transfer pump is a fixed displacement gear pump.

Illustration 1	g00350754
Fuel system schematic (typical example)

The fuel flows from the fuel transfer pump through the cored passages of the Electronic Control Module (ECM). This cools the module. The ECM can also be air cooled.

Illustration 2	g00452569
Manual fuel priming pump on left side of engine

Illustration 3	g01135517
Electric fuel priming pump on right side of engine

The fuel then flows through a fuel filter before entering the fuel supply manifold. A fuel priming pump is located on the fuel filter base in order to fill the system. An electric fuel priming pump may also be used. Refer to Illustration 2 and to Illustration 3.

The system must be primed after the filter changes. The system must be primed after draining the fuel supply and return manifolds, when the fuel injectors are replaced.

The fuel flows continuously from the fuel supply manifold through the fuel injectors. The fuel flows when either the supply or the fill port in the injector is not closed by the injector body assembly plunger. The fuel that is not injected into the cylinder is returned to the tank through the fuel return manifold.

A pressure regulating valve is at the end of the fuel return manifold. The pressure regulating valve controls the entire fuel system pressure. This provides proper filling of the fuel injectors.

The electronically controlled mechanically actuated fuel injector system provides total electronic control of injection timing. The injection timing is varied in order to optimize the engine's performance.

The timing ring is part of the rear gear group. A signal is generated by the engine speed/timing sensor. This information is for detection of crankshaft position and for engine speed. Other information and this data allows the ECM to correctly send a signal to the injector solenoids. The fuel injector's solenoid is energized in order to begin fuel injection. The fuel injector's solenoid is de-energized in order to end fuel injection. Refer to Systems Operation, "Fuel Injector".