How Do I Know It’s Time to Replace My Spark Plugs?

An engine that misfires — meaning the spark plugs fire at the wrong time — could be due to worn or fouled plugs. Other indications of worn spark plugs are low fuel economy, hard starting and sluggish acceleration. Most plugs, though, should last at least 100,000 miles before needing to be changed. In addition, engine computers do a remarkable job of compensating for worn plugs, so they might not be the main or only cause of engine problems.