What about the engine speed is unstable ?

 The engine speed is unstable. That is to say, when the engine is running, although the accelerator pedal is fixed at a certain position, the speed of the engine still changes periodically in a large range; and it takes a long time to increase the speed during acceleration. And the power is insufficient; when decelerating, it takes a long period of time to release the accelerator pedal to reduce the speed, that is, the acceleration or deceleration response is slow, the speed change is not timely, and the engine is powerless.


The essence of the unstable engine speed is the deterioration of the speed control function. The main reason is that the resistance of the moving parts inside the fuel injection pump and the generator governor is too large or the matching clearance is too large, which reduces the sensitivity of the governor, and the change of the circulating oil supply lags the change of the speed. The reasons are as follows:

  • The fuel injection pump fuel volume adjustment lever is not flexible in movement.
  • The axial clearance of the camshaft of the fuel injection pump is too large.
  • The clearance between the fork fixed on the fuel injection pump adjusting rod and the adjusting arm is too large (the clearance between the oil quantity adjusting rod and the ring gear is too large).
  • The oil supply adjustment rod and fork (ring gear and plunger rotating sleeve) are loose or deformed, which hinders the timely adjustment of the circulating oil supply.
  • The engine oil inside the generator governor is too dirty, too little or too thick.
  • The moving parts in the generator governor are too tight, and the resistance is large.
  • The joints of the moving parts in the generator governor are too worn and loose.
  • The generator governor spring is deformed or broken.
  • The adjustment distance of the flyweight of the engine governor is inconsistent.

Diagnosis and treatment methods

  •  First check whether the oil in the governor is too little, too dirty or too sticky. If the amount of oil is insufficient or too dirty or too sticky, the cause of the failure should be checked and eliminated.
  • If the quantity and quality of the oil meet the requirements, the inspection window cover of the fuel injection pump can be removed, and the oil volume adjusting rod (or gear rod) can be pinched by hand to move the rod (or gear rod) back and forth to check its tightness (applicable to A type pump).
  • If the movement resistance of the oil adjustment rod is large, it means that the rod (or gear rod) is too tight with the support hole, or is bent, deformed, pulled or corroded, or is stuck by foreign objects, and the movement is inflexible. The governor cover should be removed, and the oil volume adjusting rod (ie, gear rod) should be disconnected from the governor, and then further confirm the movement resistance of the oil adjusting rod. If the resistance is still large, it means that the above inspection is correct, and it should be disassembled and eliminated; if it can move back and forth freely within a small range, it means that the tie rod (that is, the gear rod) is bent and deformed, and the gear ring is deformed, and it should be replaced for repair or correction.
  • If the tie rod moves freely after being disengaged from the governor, the fault is in the governor.
  • If the lever for adjusting the oil volume can be moved back and forth easily by holding it by hand, it means that the clearance of the fittings is too large or the fixing screws are loose. If you hold the fork (or ring gear) with one hand while moving the tie rod (or gear rod) back and forth, and feel a relative movement, it means that the screw is loose and should be tightened. Excessive backlash between the gear rod and the ring gear can also cause the engine speed to be unstable.
  • If the above inspection results are normal, it means that each connection point of the governor is loose, such as the connection between the fly hammer pin hole seat frame, the connection between the tie rod (or tooth rod) and the speed control lever, etc.
  • Check whether the spring of the engine governor is deformed, and whether the retraction and extension distances of the flyweights are consistent. Otherwise, it should be adjusted until the corresponding flyweight retraction and retraction distances are equal.
  • Finally, check the camshaft axial clearance.
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