During a cold cylinder check, how is the cylinder that is not firing identified?

• A. The exhaust stack near the cylinder head that is not as hot as the others indicates the non-firing cylinder.
• B. The cylinder with the hottest exhaust.
• C. A visual inspection of spark plugs.
• D. An audible difference in exhaust sound.

Answer: (A)

During a cold cylinder check, you identify the non-firing cylinder by comparing exhaust temperatures. The exhaust stack from the cylinder that isn’t firing will be cooler than the others because there’s no combustion heat being produced there. The firing cylinders exhaust hot gases, so their stacks feel hotter in comparison. Relying on the hottest exhaust would point to the firing cylinder, not the non-firing one, and visual spark plug checks or listening differences aren’t as reliable for this specific test.