The reciprocating motion of the plunger in the plunger sleeve completes the oil suction and pressure of the fuel injection pump. When the plunger is in the lower position, the two oil holes on the plunger sleeve are opened, the inner cavity of the plunger sleeve is connected with the oil passage in the pump body, and the fuel is quickly filled into the oil chamber. When the cam is crowned on the roller of the roller body, the plunger rises. From the beginning of the plunger upward movement until the oil hole is blocked by the upper end of the plunger. During this period, due to the movement of the plunger, the fuel is squeezed out of the oil chamber and flows to the oil channel. So this lift is called a pre-trip. When the plunger blocks the oil hole, the oil pressure process begins. When the plunger goes up, the oil pressure in the oil chamber rises sharply. When the pressure exceeds the spring elasticity and the upper oil pressure of the oil outlet valve, the oil outlet valve is jacked out and the fuel is pressed into the fuel pipe and sent to the injector.

The time when the oil inlet hole on the plunger sleeve is completely blocked by the upper end face of the plunger is called the starting point of theoretical oil supply. When the plunger continues to move upward, the oil supply also continues. The oil pressure process lasts until the helical inclined edge of the plunger lets the plunger sleeve return to the oil hole. When the oil hole is opened, the high-pressure oil flows back to the oil channel of the pump through the longitudinal groove on the plunger and the oil return hole on the plunger sleeve. At this time, the oil pressure of the plunger sleeve chamber decreases rapidly, the oil outlet valve falls back to the valve seat under the action of the oil pressure in the spring and high-pressure tubing, and the injector stops injecting oil immediately. At this time, although the plunger continued to ascend, but the oil supply has been terminated. The time when the upper return hole of the plunger sleeve is opened by the oblique side of the plunger is called the theoretical oil supply terminal point. In the whole process of plunger upward movement, only the middle stroke is the oil pressure process, which is called the effective stroke of plunger.

In order to meet the requirements of diesel engine load, the fuel supply of fuel injection pump must be able to adjust in the range of maximum fuel supply (full load) to zero fuel supply (parking). The adjustment of fuel supply is realized by the simultaneous rotation of all plungers of the fuel injection pump by means of the gear rod and the rotating sleeve. When the plunger rotates, the start time of oil supply is unchanged, while the end time of oil supply is changed due to the change of the position of the return hole of the plunger sleeve caused by the inclined side of the plunger. As the piston rotates at different angles, the effective stroke of the plunger varies, so the fuel supply varies.

The larger the rotation angle of the plunger for the non-oil supply level 1, the greater the distance between the upper end of the plunger and the inclined side of the opening of the return hole of the plunger sleeve, and the larger the oil supply. If the rotation angle of the plunger is smaller, the oil break will start earlier and the oil supply will be smaller. When the diesel engine stops, the oil must be cut off. Therefore, the longitudinal groove on the plunger can be transferred to the oil return hole directly opposite the plunger sleeve. At this time, during the whole plunger stroke, the fuel in the plunger sleeve has been flowing back through the longitudinal groove and the return hole, and there is no pressure process, so the fuel supply is equal to zero. When the plunger rotates, the fuel supply is adjusted by changing the time of the end point of the fuel supply. This method is called the end point adjustment method.

According to the requirements of the diesel engine, the pump should ensure that the starting time of each cylinder is the same, that is, the advance angle of each cylinder is the same, and the continuation time of the fuel supply should be the same. At the beginning of the emergency speed of the fuel supply, the stop of the fuel should be swift and sharp, so as to avoid dropping oil. According to the different combustion chamber form and the method of mixture formation, the fuel pump must provide enough pressure fuel to the injector to ensure good atomization quality.