Red Seal Automotive Service Technician Practice Exam

What effect do worn spark plugs have in an engine?

1. They increase engine speed

2. They cause misfiring and reduce fuel efficiency

3. They improve fuel quality

4. They decrease engine temperature

The correct answer is: They cause misfiring and reduce fuel efficiency

Worn spark plugs significantly impact engine performance by causing misfiring and reducing fuel efficiency. As spark plugs wear out, their ability to create a strong spark diminishes. This can lead to incomplete combustion of the air-fuel mixture in the engine's cylinders. When misfiring occurs, the engine may run roughly, leading to poor acceleration and power loss. Additionally, the reduced efficiency of combustion means that more fuel is required to achieve the same power output, which directly decreases fuel economy. Therefore, the condition of the spark plugs is critical for optimal engine performance. Regular inspection and replacement of spark plugs are essential maintenance tasks that can help ensure the engine runs smoothly and efficiently.