Steps
- Look for black, fuzzy soot on the insulator. The presence of this soot, or carbon build up, reveals the presence of fuel that is rich. Readjust the carburetor so that a full burn is achieved, resulting in no carbon deposits being left on the insulator nose of the plug.
- See if there are white deposits on the insulator. This probably indicates oil consumption. If you see this, check the vehicle's valves, piston rings and cylinders for issues.
- Check for an insulator that has white or light tan blisters. This may indicate a fuel that is too lean. Try adjusting the carburetor and, if that does not fix the issue, checking for a vacuum leak.
- Be on the look out for small, black, pepper-looking spots on the nose, which indicate light detonation. If the condition is severe, the plug insulator might have a crack or chip in it. This can also cause damage to your intake valves and pistons. Make sure the spark plug you are using is the correct heat range for the vehicle and that the fuel being used is the correct octane level. Check that your timing is set properly.
- Change your spark plugs on a timely basis. Old plugs show their wear by the center electrode being rounded or worn down. This can cause the vehicle to misfire or have difficulty starting. A worn spark plug keeps the car from getting its optimum fuel economy. If left unfixed, the old plug can lead to damage in other parts of the ignition system.
- Find the issues behind melted spark plugs quickly. A melted plug could be the result of improperly set timing, where the timing is too early. It could also be a problem with the valves, distributor, too much residue on the combustion chamber, bad fuel or the spark plug's heat range may be too low.
- Read a good spark plug. A good spark plug will have no build ups or deposits on it and no worn or damaged spots. Look at the coloration of the ground strap to see if the heat range is accurate. Any color change near the end of the strap indicates that the heat range is too cool, that the heat is being absorbed too quickly to provide a good burn. Color change that occurs too close to where the strap connects to the base reveals a range that is too hot. The color transition should occur half way down the ground plug. One of the threads on the plug might also show some discoloration.
Article provided by wikihow the wikihow manual. Please edit this article and find author credits at the original wikiHow article on How to Read a Spark Plug. All content on wikiHow can be shared under a Creative Commons license.
