Over throttle occurs in diesel engines when more fuel is injected than can be burned. Which of the following is a common sign?

• A. Oil dilution
• B. White smoke from the exhaust
• C. Additional fuel consumption
• D. Black smoke from the exhaust

Answer: (D)

When a diesel engine receives more fuel than it can burn with the available air, the excess fuel doesn’t burn fully. That unburned fuel and the resulting incomplete combustion produce a lot of soot, which shows up as black smoke from the exhaust. So black smoke is the telltale sign of over-fueling. White smoke would point to other issues like coolant entering the combustion chamber or conditions of a cold start. Oil dilution can happen with prolonged rich running, but it’s a secondary effect rather than the immediate, noticeable symptom. Additional fuel consumption may occur, but the most diagnostic clue here is the black exhaust indicate of excess fuel.