When a vehicle has problems starting, idles roughly, the engine misfires or surges, lacks acceleration or has a noticeable decrease in fuel efficiency, the spark plugs may not work properly. Spark plugs may cease working because of age and normal wear and tear, but a visual inspection of the plugs can identify other problems that may have caused the failure. If the problems are not fixed, new spark plugs may fail similarly.
Make sure to inspect all of the spark plugs because a problem could be isolated to just one cylinder and cause significant engine damage. If the ceramic insulation on the plug has a red coating, this is an indication of additives in lower quality fuel and not a sign of an engine problem.
Plugs with a shiny coating on the tip or side electrode could be fuel fouled or heat damaged. Make sure the spark plugs are the correct heat range for the vehicle and if they are, have the fuel injection system check to ensure it is not running too rich.
Detonation damage indicates that your car needs a tune-up and carbon fouling which blackens the tip and the side electrode can indicate bad wiring or a leaky fuel injector. If the plug is firing too soon from preignition, the side electrode is burned away and if it has physical damage and dents to the tip it has been screwed in too deeply and is being beaten by the piston.