Which condition requires replacing a spark plug?

• A. Worn spark plugs
• B. Shows signs of arcing
• C. Misfiring
• D. Contaminated fuel

Answer: (B)

Arcing on a spark plug means the high voltage spark is leaking past the intended path, usually because the insulator is damaged, the electrode gap has become distorted, or the plug has some form of insulation breakdown. When you see arcing, the plug can no longer contain the electrical discharge reliably, which leads to weak or inconsistent ignition. Replacing the plug restores a proper gap and insulation, ensuring a solid, controlled spark and preventing misfires or engine damage. Other conditions like wear or fouling indicate problems too, but arcing is a clear, replace-now indicator that the plug has failed.