Question 108Motor Plants - QMED

The correct answer is C) clogged air intake passages. Black smoke exhausting from a diesel engine indicates incomplete combustion, which is typically caused by insufficient air reaching the engine. Clogged air intake passages restrict the amount of air available for combustion, leading to an overly rich fuel mixture and incomplete burning of the fuel. This results in the production of black smoke. The other options are incorrect because water in the fuel (A) would cause misfiring or stalling, insufficient fuel (B) would result in loss of power, and burning lubricating oil (D) would produce blue-gray smoke rather than black smoke.