(1) Causes of Diesel Engine Runaway Caused by Excessive Diesel Supply
① The ball head of the plunger adjusting arm or rack adjusting arm fails to fit into the groove of the adjusting fork, leaving the plunger at the rated fuel supply position.
② Inflexible rotation of the fuel pump plunger. This is a common cause of diesel engine runaway. The plunger remains at the rated fuel supply position and cannot be pulled by the governor, resulting in rising speed and failure of the governor to control fuel delivery.
Reasons for inflexible plunger rotation:
The plunger is damaged by collision during assembly;
Dirt inside the fuel pump allows impurities to enter the clearance of the plunger pair;
Excessive tightening torque of the delivery valve seat causes deformation of the plunger sleeve;
The gasket on the plunger sleeve positioning screw is too thin, and the positioning screw presses against the plunger sleeve to cause deformation;
The plunger sleeve positioning screw is too long or bent, locking the plunger sleeve during assembly.
③ After the fuel injector is worn, a large amount of return oil connected to the intake pipe is sucked into the cylinder, leading to excessive fuel in the cylinder.
④ Excessive and overly viscous grease is applied on the steel balls during governor installation, making it difficult for the steel balls to fly outward when the engine speed rises.
⑤ No alignment marks on the rack and gear ring, incorrect assembly, or reversed installation of the plunger.
⑥ Low fuel injection pressure leads to excessive fuel supply to the cylinder.
⑦ Sticking of the connecting rod and moving parts of the governor.
⑧ Improper governor commissioning.
Causes include:
Operators intentionally increase the pre-tightening force of the governor spring of single-cylinder diesel engines;
The action point of the No.Ⅱ fuel pump governor is set too high, resulting in high fuel cut-off speed or failure to cut off fuel;
Excessive lubricating oil or overly high lubricant viscosity inside the governor.
(2) Causes of Diesel Engine Runaway Caused by Engine Oil
① Excessive engine oil in the air filter is sucked into the cylinder.
② Overfilled oil in the oil pan blows into the cylinder during operation.
③ Clogged crankcase vent hole causes air pressure buildup, forcing engine oil into the combustion chamber.
④ Severe tilting of horizontal diesel engines allows engine oil to flow into the valve chamber; engine oil is then sucked into the combustion chamber when the clearance between the valve and valve guide is excessively large.
⑤ Severe wear of piston rings, excessive cylinder liner clearance, or aligned openings of piston rings cause a large amount of engine oil to blow into the combustion chamber.
⑥ Overly thin engine oil easily enters the combustion chamber.
Reasons for diluted engine oil:
Diesel leakage into the oil pan;
Overhigh operating temperature of the diesel engine;
Substandard engine oil quality.
⑦ Clogged oil control rings and oil return holes on the piston cause engine oil to blow into the combustion chamber.
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Post time: May-11-2026