During main engine performance testing it is noticed that one cylinder has firing and compression pressures lower than average. Which of the following would most likely be the cause?

Correct Answer: Option C — Worn piston rings

Worn piston rings and compromised cylinder liners allow combustion gases and charging air to blow past the piston into the crankcase during the compression stroke. This blow-by directly causes a noticeable drop in both peak compression and subsequent firing pressures.