Lead-fouled: You'll find a brown/yellow glazing on the insulator nose. At high loads, the glazing becomes conductive and causes misfiring. Caused by lead additives in fuel.
Cracked insulator nose: Most of the time this is caused by mishandling the plug vis--vis dropping it, although overuse can also cause this. The result can be that the spark arcs at a point that is inaccessible for the fresh charge of air/fuel mixture, thus causing a misfire.
Since some problems can be cylinder-specific, it's important to keep track of what plug came out of what cylinder. Remember that if the engine is in good shape, all of the plugs should exhibit the same electrode erosion and light tan or gray color. Plugs that differ in appearance are indicative of a problem with a given cylinder. However, all of the plugs may show the same problem, if let's say, a throttle body or carburetor is misadjusted or faulty. The upside is that by reading your spark plugs, you may catch a problem in the early stages before it leaves you stranded or your wallet drained.
Part 2: Plugs Go High-TechA plug is a plug, right? Well, that may have been true 20 years ago, but over the past several years' spark-plug technology has made a gargantuan leap forward as manufacturers have worked to improve the ignition of fuel inside the combustion chamber. The result is a variety of plugs, many of which are infused with fascinating technology. Just as the Big Three have a slightly different way of designing their fullsize pickups, for instance, spark-plug manufacturers seem to approach their plugs differently. Some are designed for longevity while others tout improved performance. The common denominator nowadays seems to include high-tech electrodes as well as super-conductive materials that last longer and help create larger, more powerful flame kernels. What this means to us 'wheelers is more power and better fuel economy by simply screwing in some plugs. Following are two examples of the latest spark-plug technology.
Problem: Improper gap This gap between the electrodes is far too small for the plug to cre
Problem: Detonation Here you can see how this form of abnormal combustion has damaged the