Correct answer
Incomplete combustion due to insufficient air or too much fuel relative to available air.
Incomplete combustion and soot production, for example insufficient air or too much fuel relative to available air. A blocked air filter, intake fault or injection problem may be causes. The symptom does not by itself identify a failed component and does not mean the engine always compensates for insufficient air by injecting more fuel. Check the cause following manufacturer guidance.
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Incomplete combustion due to insufficient air or too much fuel relative to available air.
Combustion that is always correct and produces no particles.
Conclusive proof that the only fault is in the engine piston rings.
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