What are the causes of diesel engine overspeed failure?
3 Answers
The causes of diesel engine overspeed failure are: 1. Malfunction of the fuel injection pump governor itself, causing it to lose its normal speed regulation characteristics. This situation is characterized by abnormal phenomena such as sticking or looseness in the fuel injection pump governor. 2. Changes in the diesel engine's speed regulation characteristics due to external factors, characterized by the absence of faults in the fuel injection pump governor itself, but additional fuel entering the cylinder for combustion during engine operation. The solutions for diesel engine overspeed failure are: 1. Quickly return the accelerator pedal to the stop position; 2. For fuel injection pumps with exposed fuel supply rods or rack bars, quickly pull the rod back to the fuel cut-off position; 3. For engines with decompression devices, quickly pull the decompression handle to the decompression position; 4. Promptly shift into high gear, depress the brake pedal, and slowly release the clutch to stall the engine; 5. Quickly loosen the high-pressure fuel pipes of each cylinder to stop fuel supply; 6. For intake pipes with valves, close the valve. If there is no valve, remove the air filter and block the intake pipe.
Having driven diesel trucks for over a decade, I can tell you that diesel engine overspeeding, commonly known as 'runaway,' mainly occurs in three scenarios: First, when the governor of the fuel injection pump malfunctions—either the spring breaks or the flyweights get stuck—it's like having the throttle jammed, causing the RPM to skyrocket. Second, if the rack or plunger of the high-pressure fuel pump gets stuck in the maximum fuel supply position, fuel is forced into the engine uncontrollably. Third, a leak in the intake system, such as a ruptured turbocharger pipe or a clogged air filter, allows a large amount of unmeasured air to flood in. Once the tachometer needle starts spinning wildly, you must immediately cut off the fuel supply by pulling the engine stop switch or blocking the intake pipe. Regular oil changes are crucial, especially for older vehicles where insufficient lubrication of the governor can easily lead to sticking.
When learning to repair diesel engines, my mentor taught me that overspeeding is mostly caused by governor mechanism failure. If the flyweights, springs, or levers inside the governor rust and seize, they become completely unable to adjust fuel supply according to engine speed. If the fuel injection pump's plunger gets stuck due to impurities, it will continuously inject excessive fuel. Turbocharger air leaks can suddenly increase air intake, causing excessively rich air-fuel mixture and loss of control. Air in the fuel lines or high water content in diesel can also trigger abnormal combustion. During repairs, I first check the governor's flexibility, then inspect the fuel pump's sealing, and finally test the turbocharger's pressure. Regular cleaning of diesel filters is recommended, as impurities in low-quality fuel are most likely to jam precision components.
