Diesel Knock (Combustion Knock)
Diesel knock is a sharp knocking noise caused by fuel igniting too abruptly in a diesel engine.
What is Diesel Knock (Combustion Knock)?
Some knocking is normal, especially when cold. Pilot injection reduces it on modern engines. Poor fuel or faulty injectors increase it. A cold diesel knocks more until combustion chambers warm up. Injector balance data in live data shows uneven cylinders.
How it works
If too much fuel ignites at once after a delay, pressure rises very suddenly and causes the knock.
Why it matters for your car
Loud knocking from one cylinder can indicate a leaking or sticking injector. Fuel with a low cetane number makes knock worse.
Other terms
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