When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
If a spark plus is going bad you will most likely develop a misfire and the engine computer will trigger a check engine light reporting a misfire was detected in a certain cylinder. But if one of the spark plugs is bad you should replace them all as the others will probably start to misfire soon under normal wear and tear.