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Diesel knock is a vibration that is caused by too rapid a pressure increase during combustion, especially cold diesels suffer from a diesel knock and as the engine gets warmer, the diesel knock will decrease

Excessive diesel knock can be caused by:

Faulty injector (s): such as dripping from the atomizer and a wrong spray pattern.

Faulty injection pump, delivery valves faulty, piston (s) worn.

Fuel: cetane number too low, water in the fuel, air in the fuel.

Motor: compression too low or faulty preheating system.