The fuel filter is connected in series with the pipeline between the fuel pump and the oil inlet of the throttle valve body. The function of fuel filter is to remove the iron oxide, dust and other solid impurities contained in the fuel to prevent the fuel system from being blocked (especially the fuel injection nozzle). Reduce mechanical wear, ensure stable engine operation, and improve reliability. The structure of the fuel injector is composed of an aluminum shell and a stainless steel bracket, which is equipped with high-efficiency filter paper in a chrysanthemum shape to increase the flow area. The electronic fuel injection filter cannot be used in conjunction with the carburetor filter. Because electronic fuel injection filters often withstand fuel pressure of 200-300KPA, the pressure resistance of the filter is generally required to reach 500KPA or above, while chemical oil filters do not need to reach such high pressure.

The structure of the diesel filter is roughly the same as that of the oil filter. There are two types of diesel filter: replaceable type and spin on type. However, its working pressure and oil temperature resistance requirements are much lower than those of the oil filter, while its filtering efficiency requirements are much higher than those of the oil filter. The filter element of diesel filters mostly uses filter paper, and some also use felt or polymer materials. In addition to filtering mechanical impurities in diesel, a diesel filter also has an important function of filtering water. The presence of water poses great harm to the fuel supply system of diesel engines, as rust, wear, seizure, and even deterioration of the combustion process of diesel. The main method of removing water in the diesel filtration system is sedimentation. Either a settling chamber is installed at the bottom of the filter, or a specialized settling device is used. Both the sedimentation chamber at the bottom of the filter and the specialized sedimentation tank are equipped with a drain valve. When water accumulates to a certain amount, the valve is opened to drain the water.