FAA Powerplant Written Practice Test

Which issue could potentially be detected by a cold cylinder check?

1. A defective fuel pump

2. A defective spark plug lead

3. An intake manifold leak

4. Oil viscosity failure

The correct answer is: A defective spark plug lead

A cold cylinder check is an important diagnostic tool used to evaluate the performance of individual cylinders in an engine. This technique involves running the engine and then using a tool like a temperature probe to check the cylinder head temperatures. When one cylinder runs cooler than the others, it can indicate that the cylinder is not combusting properly. In this context, a defective spark plug lead could lead to an issue where the spark plug is not firing correctly. This would result in that cylinder not reaching the same temperature as the others due to incomplete combustion, making it potentially detectable during a cold cylinder check. By contrast, a defective fuel pump or an intake manifold leak could impact multiple cylinders, affecting overall engine performance rather than isolating an issue to one cylinder. Oil viscosity failure generally pertains to the lubrication system and does not directly relate to a cylinder's combustion efficiency. Therefore, the most pertinent issue that can be detected by a cold cylinder check would be the condition of the spark plug lead, as it directly impacts the combustion process of that specific cylinder.