Maintenance Technician Practice Test 2025 – 400 Free Practice Questions to Pass the Exam

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What does an imbalance in the fuel-oxygen ratio indicate?

Efficient combustion

Black exhaust smoke

An imbalance in the fuel-oxygen ratio is typically indicative of incomplete combustion, which can result in black exhaust smoke. When there is too much fuel in relation to the amount of oxygen, the combustion process does not fully burn the fuel. This unburned fuel then exits the engine, leading to the characteristic black smoke in the exhaust.

In contrast, efficient combustion occurs when the fuel and oxygen are properly balanced, producing minimal emissions. White exhaust smoke can indicate other issues, such as coolant leaking into the combustion chamber. Excess oxygen can occur in scenarios where there is a lean fuel mixture, but this would not produce black smoke. Therefore, the presence of black exhaust smoke serves as a clear signal of an imbalance, specifically one that favors excess fuel.

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White exhaust smoke

Excess oxygen

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