BreakageĪppearance & Symptoms: The insulator around the center electrode may be broken (see left) or the ground electrode may be bent. Possible Causes: This condition commonly occurs when gasoline contains too much lead however, because spark plugs are changed frequently in racing applications, lead fouling has become less common. Lead fouling can cause your engine to misfire only at high-rpm and under hard acceleration. Lead fouling generally shows up as yellowish brown deposits on the spark plug’s insulator nose. Lead FoulingĪppearance & Symptoms: Lead fouling can only occur in applications that use leaded gasoline, such as racing engines.
Other possible causes could be low compression, vacuum leak, overly retarded timing, or improper spark plug heat range. Dry fouling, or carbon fouling, is often caused by an overly rich condition, and the problem may lie with your air cleaner (clogged) or carburetor. Possible Causes: Depending on whether the spark plug is coated in oil or fuel, wet fouling can be symptomatic of a compromised head gasket, poor control from your pistons’ oil control ring, valvetrain problems, or an extremely rich condition. Both conditions can create poor starting and misfiring. Wet fouling (bottom) has a wet, sometimes oily appearance. Possible Causes: Oil leaks, poor fuel quality.Īppearance & Symptoms: Dry fouling (top) appears as sooty, black build-up. This build-up of combustion deposits can eventually (but not usually) fill in the space between the two electrodes. As a result of this masking of the electrodes, your engine may experience a misfire. DepositsĪppearance & Symptoms: The electrodes-center and ground-are covered in an ashy coating. NormalĪppearance: A light tan/gray or brownish color, along with very little electrode erosion, indicates optimal operation conditions, including a healthy engine and correct spark plug heat range. Check out the images below, courtesy of NGK Spark Plugs, and get ready to do a little light reading the next time you pull your spark plugs.
#How to install spark plugs correctly how to#
With help from the spark plug experts at NGK, we’ll teach you how to diagnose minor tuning issues or potentially major engine problems by examining your spark plugs. The trick is learning how to read your spark plugs. Is your engine running too lean? Too rich? Is there an issue with oil control or ignition timing? Or is everything just fine with your engine? Like the mechanical version of the Magic 8-Ball, your spark plugs may have the answers for you. Listen closely because your spark plugs may be trying to tell you something.