(1) Rotate the crankshaft of diesel engine by hand. If you can't hear the sound of fuel injection from the fuel injector, or if there is no fuel flowing out or the oil flow is discontinuous when unscrewing the bleed screw on the fuel injection pump, a large amount of oil foam and bubbles will appear, which indicates that the fuel pressure is too low or there is no fuel coming, which belongs to the fuel supply system fault. At this time, check one by one. If there is no fuel in the fuel tank, the oil drain switch is not opened, the oil pipeline is blocked or air enters into the oil pipeline, the filter element of the fuel filter is blocked, and the oil pipe joint is loose, the targeted measures can be taken according to the identified causes and timely eliminate them.

(2) When cranking the crankshaft by hand, if you feel that the pressure of the cylinder compression stroke is very low, and you can hear the hiss in the intake pipe or the exhaust pipe, it shows that the sealing of the inlet and exhaust valves is not tight, resulting in serious air leakage, which belongs to the fault of the valve train. If the valve leakage, if the valve clearance is too small, the valve clearance can be readjusted; if the valve spring is broken or its elasticity is insufficient, it is necessary to replace the valve spring; if the sealing ring of the valve head and valve seat is seriously ablated, the valve seat shall be reamed and polished, and then the valve head shall be carefully ground with valve sand. In some cases, the valve shall be replaced and the valve seat shall be re inserted.

(3) If you feel that the compression force of the engine is insufficient, you can hear the "hissing" air leakage sound at the oil filling port of the crankcase when you rotate the crankshaft by hand, which indicates that the cylinder has the problem of air leakage and pressure relief in the compression stroke, which belongs to the fault of the crank connecting rod mechanism. In this regard, the wear of piston, piston ring and cylinder sleeve should be checked to see if the fitting clearance is too large due to wear, resulting in air leakage of cylinder; if the sound of air leakage is not heard at the oil filling port, but the cylinder pressure is too low, check whether the cylinder head bolts are loose, whether the cylinder is too thick or burned through by high temperature gas; it may also be caused by serious deformation of the joint surface of cylinder block and cylinder head

Air leakage due to loose sealing. After finding out the causes, effective measures can be taken to repair the corresponding parts or replace them with new ones.

(4) Although the sound of fuel injector can be heard when cranking the crankshaft by hand, the engine cranking resistance is too large to meet the requirements of starting speed and is difficult to start. This is mostly due to fuel supply system or crank connecting rod mechanism failure. Such as: insufficient fuel supply, cylinder seals excessive wear, or lubricating oil is too thick. When starting the engine, the condition of "temperature" should not be ignored, especially in the winter of northern China, when the temperature is low, the diesel oil becomes bigger and the fluidity becomes worse, which is not conducive to atomization; the air temperature entering the cylinder is low, which affects the spontaneous combustion of combustible mixture, the lubricating oil becomes thicker, and the running resistance of starting stage increases. Therefore, the engine should be preheated before starting in winter, such as filling the radiator with hot water, heating the oil pan and cylinder block with dark fire or blowtorch. In addition, improper adjustment of pressure reducing mechanism or failure of pressure reducing mechanism will lead to diesel engine start-up difficulty due to many unsuccessful start-up of diesel engine and excessive diesel accumulation in cylinder. Therefore, the decompression mechanism should be checked regularly and adjusted if necessary. If there is any defect, it should be repaired or replaced in time.

(5) When starting the diesel engine, if the exhaust pipe emits black smoke, or some white smoke, or it seems to have caught fire but the explosion sound is not coherent, it can be diagnosed that there is a fault in the fuel supply system. For example: poor fuel atomization, air or moisture mixed in the oil circuit; or the fuel supply time is not correct, check and adjust the fuel supply time of the diesel engine. If the diesel engine is still difficult to start, it is necessary to check the fuel injector and the injection pump to find out the causes of the difficulty and eliminate them.