FUEL SYSTEM

There are two methods to feed fuel into the combustión chamber; the first one is pre-combustion. In which the fuel begins the ignition in the pre-combustion chamber before entering the cylinder;

And the second is by direct injection,  in which the fuel is directly injected into the cylinder for combustion. 

It is also important to understand that the injection pumas which are used in many recent Cat. Motor models. The injection pumps employ a direct method of injection to feed the fuel which is different than that of the traditional pre-combustion and direct injection motor systems. 

Basically, the fuel circulates in the same manner up to the moment of injection of fuel. (1) The fuel moves itself from the tank, (2) by a water separator, (3) by the primary fuel filter, and (4) towards the fuel transference pump. The primary filter could be located before or after the transfer pump. The fuel goes from the fuel transfer pump (5) to the secondary filter, and then (6) to a fuel injection pump (pre-combustion and direct injection) or a fuel injection pump.