Why is Cummins engine generator no idle speed

by Generator D. Diesel Generator

The engine has no idle speed. Generally, the throttle is turned off when it is placed at the idle position. When the throttle is slightly enlarged, the speed is increased quickly and cannot be stably operated at a low speed.


a. The governor idle spring is too soft or broken.

b. The governor sensing element is worn too much.

c. The plunger of the fuel injection pump is seriously worn.

d. The temperature is too low.

e. The cylinder pressure is too low.

Diagnosis and treatment

a. There is no idle speed at cold start, which is generally a normal phenomenon. This is because the temperature is too low, the viscosity of the oil is too large, the internal resistance of the engine is increased, the spray and evaporation conditions of diesel oil become worse, resulting in the engine can not maintain the minimum stable speed operation, when the throttle is raised, it will turn off quickly. In this case, the throttle can be adjusted to run at a slightly higher idle speed, and then resume idle operation after the engine heats up.

b. If the engine has been used for a long time, there is no idling condition, and the fuel consumption is not normal due to insufficient power. It is generally the plunger wears too much, and the oil leakage increases at idle speed, so that the oil supply cannot meet the idle speed requirement; or the cylinder pressure is too low, the fuel injection advance angle is too large, too small, resulting in poor engine combustion conditions. As long as according to the insufficient power treatment, the idle condition will naturally recover.

c. If the above conditions are normal, the idle working element of the governor should be considered for abnormality. Check if the governor spring is broken or the governor is too worn or the spring is too soft, so that the centrifugal force of the flying hammer during idle operation is much greater than that of the spring tension and reduce oil, or the maintenance personnel do not adjust properly. The fuel injection pump assembly must be removed and the maintenance adjustments must be repeated on the test bench.

d. When checking the governor, first adjust it with the idle screw. If the adjustment is invalid, adjust the pre-tension force of the idle spring. The idle spring adjusting nut can be slightly screwed inward or a washer is placed on the spring seat to increase the preload and increase the idle speed. If the spring is broken, it should be replaced and then adjusted to restore the idle working performance.

Hope above information is helpful to you. Starlight Power not only provide technical support of diesel genset, but also a manufacturer of diesel generator with 46 years' experience. Welcome to call us by phone +8613481024441(same as WeChat) or Whatsapp +8613471123683, we will work with you.

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About Generator D. Senior   Diesel Generator

108 connections, 1 recommendations, 652 honor points.
Joined APSense since, September 11th, 2017, From Jiangsu, China.

Created on Nov 19th 2020 19:16. Viewed 146 times.


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