Spark Plug Diagnosis

In times past, one of the easiest maintenance items on a vehicle was checking and changing the spark plugs. That was before engine compartments became shrouded in emission's tubing and computerized sensors. If you're lucky enough to have an automobile where the plugs are relatively easy to reach, take advantage of it. That's because they offer telltale indications of what's going on in the combustion chamber and the internal health of your engine.


Before you begin ratcheting out your plugs in search of suspicious symptoms, a few words of caution: First, be sure to check ALL of the plugs. There could be a serious problem brewing in just one cylinder that you wouldn't want to overlook. Second, if your plugs indicate a problem that's related to the plug's heat range or the plug is simply worn out, you can fix these problems with a new, and correct, set of plugs. If the diagnosis is more serious, though, and your plugs are oil-foiled because of a worn piston ring, new plugs won't make the worn ring go away. Get the vehicle to your mechanic for the overhaul, then replace the plugs.


The following is a comprehensive list of conditions which you may find when you pull spark plugs:

Signs
Normal: When the engine is running the way it should, normal-reading plugs will look pretty much the same way they did when they were new and first screwed into the engine block.


Normal, but with red coating: The red coating is a result of the additives in lower-quality unleaded fuel and will be visible on the plug's ceramic insulation. The red coating is not an indication of any engine problems.