Engine Weakness-7 Most Important Failure Analysis
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Fault Analysis And Troubleshooting Of Engine Weakness

In addition to overcoming the friction resistance of various parts of the engine and driving various auxiliary devices (such as water pump, fuel injection pump, fan, air compressor, generator, oil pump, etc.), the force generated by the combustion of fuel in the engine cylinder and the work done by gas expansion finally outputs the power outward through the flywheel.

  • If the heat generated in the cylinder of the engine is small, the thermal efficiency is not used high, the self-friction resistance is too large, or the power consumption of driving auxiliary devices increases, the output power of the engine will be reduced and the engine weakness will appear weak. The reasons for the above phenomena are engine weakness:

Cause Analysis Of Engine Weakness

 Insufficient oil supply causes engine weakness

  • The fuel system shall be able to spray fuel with good atomization into the cylinder in a timely and appropriate manner. If there is a fault in the fuel system and the amount of oil injected into the cylinder is small, the heat generated by combustion will be reduced. When the heat is reduced to the point that it cannot meet the requirements of engine load, the engine will be powerless against engine weakness.

Poor spray quality causes engine weakness

  • When the engine is working, the spray quality of the injector is poor, so the fuel surface area injected into the cylinder is small, and the oxygen binding rate is reduced. Even if the amount of oil injected into the cylinder is very large, the quantity of heat emitted by the cylinder is low due to the poor atomization quality and little oxygenation reaction of engine weakness.

Effect of injection advance angle

  • The amount of fuel injected into the cylinder shall be appropriate. If the pressure rise rate of fuel increases in the fast tender period, it is easy to cause rough engine operation. The rough operation will consume part of the power, that is, the utilization of thermal efficiency is not high, and the effective power output will be reduced. The injection advance angle is too small, and most of the combustion process moves to the expansion work process, which reduces the pressure rise rate, the maximum pressure, the exhaust temperature, more heat loss of cooling water and significantly reduces the thermal efficiency.

Effect of inflation

  • The fuel can burn in the cylinder, which is mainly due to the heat released by the chemical reaction between carbon atoms and oxygen atoms in diesel (generating carbon dioxide). If the cross-section of air circulation is reduced due to the blockage of the air filter (the intake volume of engine turbocharger with a turbocharger is reduced due to miasma) or the influence of the valve mechanism, resulting in insufficient inflation of the engine, As a result, the carbon atoms in the fuel cannot fully react with the oxygen atoms, so the heat released is reduced and the engine is powerless of engine weakness.

Poor sealing of parts containing working medium

  • If the cylinder gasket is damaged, the valve is not closed tightly, and the matching clearance between the piston and the cylinder wall is too large, it can cause air leakage and poor compression, resulting in poor combustion effect of fuel in the cylinder and weak engine of engine weakness.

Effect of ambient temperature

  • When the ambient temperature is too high, it will often cause the engine to overheat. Under the dual action of high ambient temperature and engine overheating, the air expands, which affects the inflation of the engine and reduces the engine power. When the ambient temperature is too low, it will cause poor evaporation of fuel in the cylinder, resulting in incomplete combustion, that is, the heat generated by the working medium in the cylinder will be reduced.

Effect of engine resistance

  • If the engine assembly is too tight and the oil is too thick, the engine resistance will be too large. In addition to overcoming its own friction and auxiliary device resistance, the power generated by the engine reduces the effective power output, that is, the engine is weak of engine weakness.

Diagnosis And Troubleshooting Of Engine Weakness

Diagnose according to the analyzed causes and fault phenomena.

  1. If the engine starts with less exhaust and is difficult to start, the reason is insufficient fuel supply in the fuel system, diagnosis and troubleshooting shall be carried out according to the faults described in the fuel system.
  2. If the engine starts smoothly, but the exhaust pipe emits black smoke, the engine speed is not easy to improve. The main reason is that there is too little air entering the cylinder. Check the air filter of the intake part (check the supercharger for the engine with the turbocharger) and eliminate it.
  3. If the engine overheats, most of them are caused by too late injection time, which is the fault cause of engine weakness and should be adjusted. The adjustment method is shown in the description of the engine’s failure to start.
  4. If the exhaust pipe of the engine emits blue and white smoke, it indicates that the weakness of the engine is caused by a cylinder blow-by, which shall be handled.

    5. Check for air leaks

  • Pry the engine flywheel to compress the piston of the inspected cylinder to the top dead center, remove the fuel injector, shift to low gear and pull off the hand brake, and then use the hose to fill the combustion chamber with compressed air from the fuel injection nozzle hole. At this time, another person listens to the sound of air leakage at the inlet pipe orifice or exhaust pipe orifice, oil filler, cylinder pad, or radiator water inlet.
  • If air leakage is heard somewhere, it indicates that the cylinder is poorly sealed. For example, the sound of air leakage at the outlet of the exhaust pipe or intake pipe indicates that the air is not tightly closed, or the sound of air leakage at the water inlet of the radiator indicates that the cylinder gasket is damaged. It shall be eliminated after identification.

   6. Check engine resistance

  • Pry the engine flywheel with a crowbar. If it feels more laborious than other diesel engines of the same type or in normal use, it indicates that the resistance of the diesel engine is too large. If the diesel engine has just been repaired, it is mostly caused by the too-tight assembly, so it should be run in or reassembled.

   7. Check valve timing

  • If the above inspection is normal, the reason for the weakness of the diesel engine may be in the valve timing phase. Then check the valve clearance of the valve mechanism and the crankshaft angle when the inlet and exhaust valves are opened or closed, and then compare it with the valve timing diagram to find out.
  • Valve timing inspection method: valve clearance adjustment shall comply with the values specified in the technical documents. Open the observation window cover of the engine flywheel housing, pry the flywheel with a crowbar to rotate, compress the piston of the first cylinder to the top dead center, make a 3-fertilizer dial and pointer, fix the dial on the belt pulley, fix the pointer on the front cover plate, and make the pointer point to the “J” of the dial.
  • Remove the valve cover, place the dial indicator and bracket on the cylinder head, start to pry the flywheel to rotate, and rotate the push rod of the valve mechanism by hand. When the push rod does not rotate, it indicates that the valve is about to open. At this time, the pointer on the dial indicates the valve opening angle; Make the contact rod of the dial indicator against the valve rocker arm (push rod end), adjust the dial indicator to zero, and then continue to rotate the crankshaft. When the pointer of the dial indicator returns to the zero position, turn the push rod by hand, from the immovable to the rotation boundary, and the valve is closed. At this time, the indication degree of the pointer on the dial is the valve closing angle.
  • The included angle turned by the crankshaft from valve opening to closing is the continuous angle of valve opening. Compare the inspection results with the valve distribution phase diagram specified in the technical documents of the machine. If the out of tolerance is large, find out the causes of the out of tolerance, such as serious wear of the transmission gear, the correctness of the installation position of the transmission gear, damage of the camshaft keyway and key, and whether the wear of the cam working surface, and eliminate them after finding out.
  • Generally, only the first cylinder of a diesel engine can be checked, and the valve timing of other cylinders is guaranteed by the camshaft.
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