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What are the causes of unstable diesel engine speed?

2 Answers

Hattie

07/24/25 4:38am

Below are the common causes of failure listed: 1. Fuel pipeline: Air enters the fuel pipeline, causing unstable fuel supply. 2. Fuel supply: The uneven fuel supply among cylinders exceeds the standard. Under idle conditions, the uneven fuel supply among cylinders must not exceed the specified range (generally 12%). Otherwise, the diesel engine may experience unstable operation during idling. If necessary, the uneven fuel supply should be adjusted on the fuel pump test bench. 3. Injection pressure difference: Excessive injection pressure difference among cylinders leads to uneven atomization quality, which also causes unstable diesel engine speed. In this case, the injection pressure should be adjusted to improve atomization quality and ensure the pressure deviation among cylinders is within the allowable range. 4. Governor: The governor's flyweight movement is not flexible. The inflexible opening and closing of the flyweights reduces the governor's sensitivity, making the diesel engine speed unstable.

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DeCamilla

08/11/25 12:16am

Last time I drove my old diesel truck for hauling, the engine RPM kept fluctuating up and down which was really annoying. The problem lies in the fuel system - air entering the fuel lines can cause unstable fuel supply, and a diesel filter that hasn't been changed for too long can get clogged. The most troublesome issue is when the governor spring gets loose; this component controls fuel injection quantity, and when it fails, the RPM jumps around. Also, when the fuel injectors have severe carbon buildup, the fuel injection becomes uneven, making the engine pant like it just ran a marathon. You should fix it immediately, otherwise breaking down halfway would be terrible. I suggest first replacing the filter and bleeding the air from the system. If that doesn't work, find a professional mechanic to check the governor - trying to fix it yourself might make things worse. Remember to maintain the fuel system regularly to avoid many headaches.

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