Which of the following can lead to a decrease in engine efficiency?

A decrease in engine efficiency is often linked to mechanical factors that can impede the normal functioning of an engine. Excessive back pressure is one such factor that has a direct negative impact on engine performance. Back pressure refers to the resistance that exhaust gases face as they exit the engine. When back pressure is too high, it can restrict the flow of exhaust gases, resulting in incomplete combustion and reduced power output. This inefficiency contributes to increased fuel consumption, as the engine must work harder to achieve the same level of performance.

In contrast, regular maintenance, proper fuel quality, and optimized cooling systems all contribute to maintaining or enhancing engine efficiency. Regular maintenance ensures that all engine components operate smoothly and wear is minimized. Using the right quality of fuel enhances combustion efficiency, while an optimized cooling system helps maintain the engine at an ideal operating temperature, preventing overheating, which can also decrease efficiency.