Diagnosis of internal leakage in fuel injection pumps: Internal leakage in fuel injection pumps is usually difficult to detect with the naked eye. If the diesel engine has difficulty starting, power decreases, there is endless air in the oil circuit, sometimes it automatically shuts off, and at the same time, the oil level inside the fuel injection pump housing or oil pan abnormally rises, it can be diagnosed as an internal leak in the fuel injection pump.
The main areas of leakage inside the fuel injection pump are as follows:
1. The installation shoulder of the plunger sleeve is leaking. The plunger sleeve of the plunger type fuel injection pump does not have a sealing gasket between the shoulder of the large cylindrical surface and the upper body of the oil pump, and sealing is achieved through fine machining of the two joint surfaces. This is a circular, small sealing plane. The appearance of obvious compression marks at this point will cause a large amount of diesel leakage, making the diesel engine unable to work properly. Sometimes, there may be a phenomenon where the engine can barely run at low speeds, but when the speed increases, it will suck in air. The main reason for the compression marks on the shoulder of the plunger sleeve installation platform is the excessive torque of tightening the oil outlet valve seat. In addition, the fluctuating stress caused by the changes in high-pressure diesel during operation can also accelerate the fatigue damage at this location.
2. Leakage between plunger and plunger sleeve. The fit between the plunger and the plunger sleeve was originally very precise, with a gap of only 0.002-0.003mm. After selection and grinding, the surface roughness and precision of the two are particularly high. In use, if diesel contains impurities and moisture, it can cause wear or corrosion of plunger components, increase clearance, and cause diesel to leak, making it impossible to establish high pressure on diesel.
3. There is oil leakage at the positioning screw of the plunger sleeve. There is a 1mm thick pure copper pad under the positioning screw of the plunger sleeve, which mainly serves as a sealing function. If this small washer is missing, or if it becomes fluffy or ruptured, the diesel inside the plunger sleeve will leak from the positioning screw.
4. Leakage of oil outlet valve. When the pure copper (or nylon) sealing gasket between the tight seat of the oil outlet valve and the large end face of the oil outlet valve seat is broken, deformed, or the tight seat of the oil outlet valve is not tightened, the high-pressure oil chamber above the oil outlet room will be connected to the low-pressure chamber below, causing the fuel injection pump to be unable to produce high-pressure diesel.
5. The return oil overflow valve is leaking. The purpose of setting a return oil overflow valve for a multi cylinder fuel injection pump is to maintain a pressure of over 150kPa for diesel fuel in the horizontal oil passage of the upper body of the fuel injection pump. If the return oil overflow valve and valve seat are worn or rusted, the valve is padded with debris, or there is a return oil phenomenon, which causes a decrease in diesel pressure at the inlet of the plunger sleeve, or draws air into the fuel injection pump, causing the diesel engine to work weakly or even automatically shut down.
6. There is oil leakage between the push rod and liner of the oil pump. When the push rod and liner of the plunger oil pump are severely worn or the sealing ring on the push rod is damaged, the oil leakage will increase significantly. If the oil drain hole is blocked, this part of diesel will be injected into the oil passage of the fuel injection pump.
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