Final answer:
A defective spark plug can be caused by contaminants, wear and tear, or incorrect gapping, leading to engine performance issues. To fix this, the defective spark plug should be replaced with a correctly specified and gapped new spark plug. Replacement involves removing the old plug and carefully installing and tightening the new one.
Step-by-step explanation:
Understanding Spark Plugs
When considering what might cause a spark plug to become defective, several factors can contribute. Common causes include oil or fuel contaminants, high mileage wear and tear, or improper spark plug gap. Symptoms may manifest as misfires, poor fuel economy, rough idling, or difficulty starting the engine. To remedy a defective spark plug, the corrective action is to replace it with a new one. When installing new spark plugs, make sure to use the correct type and gap for your vehicle as specified by the manufacturer.
Replacement typically involves the following steps: carefully removing the ignition coil or spark plug wire, using a spark plug socket to remove the old spark plug, checking and setting the appropriate gap on the new spark plug, and installing the new spark plug by screwing it in by hand to prevent cross-threading before carefully tightening to the manufacturer's specified torque.