For spark plugs with normal gasoline engine operation, the surface of the porcelain core should be white, but due to differences in fuel and additives, some of the surface of the porcelain core is yellowish, reddish or reddish-brown. If the gasoline engine malfunctions, the surface color of the porcelain core will become pale, slightly black and brownish black. From these different colors, different faults of the gasoline engine can be judged. 1. The porcelain core is white. The porcelain core is white, the central pole is fused or chipped, the tip of the side pole is thin and the surface is rough, and the surface of the shell protruding into the cylinder has metal peeling and the like, which indicates that the spark plug is overheated. In a multi-cylinder gasoline engine, it only appears on individual spark plugs. It may be because the spark plug's thermal value (heat type) is too low, misuse, poor quality, etc.; if the porcelain core is often white in a certain cylinder, the compression ratio of the cylinder should be checked. Check if the water jacket around the spark plug is blocked. For high compression ratios, attention should be paid to whether there is a hot ignition phenomenon; if several cylinders have white porcelain core at the same time, the load of the gasoline engine should be taken into account and the capacity of the cooling system should be insufficient. The spark plug with higher heat value should be used instead. 2, ceramic core was slightly black. It is slightly black and covered with a thin layer of charcoal. The shell torus and even the side electrodes are charred. If this phenomenon occurs after a long period of cold car and low speed operation, it will be eliminated after a period of normal use. If the normal operating conditions are high, replace the low-heat spark plug. After replacement, attention should be paid to whether the spark plug is overheated, the center pole is melted, and the cylinder is pulled when the gasoline engine is at high speed and high load. 3, porcelain core was brownish black. Spark plugs are dark brown in color and have a thick, hard blocky coke on the shell and side poles. This is the performance of the gasoline engine burning oil. The oil enters through the piston ring or intake valve duct. Sometimes it is not the cause of the burning oil but the spark plug itself. It is obvious that the porcelain body is broken or the side electrodes are broken. There are also obvious reasons. Inspection method: Place the spark plug on the cylinder head, use the central high-voltage wire from the spark plug connector bolt about 5mm, and then dial the breaker contacts to see the sparkover of the spark plug gap. If the spark is intense and blue-white, it indicates that the spark plug is normal. If the spark is weak or there is no spark, the spark plug itself is faulty and should be replaced.