Generally, spark plug issues can lead to poor engine performance, resulting in abnormal phenomena such as difficulty starting, unstable idle, poor acceleration, backfiring during sudden acceleration, excessive exhaust emissions, and increased fuel consumption. A spark plug mainly consists of a terminal nut, insulator, terminal stud, center electrode, side electrode, and shell. Spark plugs are installed on the side or top of the engine. In earlier designs, spark plugs were connected to the distributor via ignition cables. However, over the past decade or so, engines in passenger cars have largely transitioned to direct connection between ignition coils and spark plugs. Under high voltage, the air between the center electrode and side electrode of a spark plug rapidly ionizes, forming positively charged ions and negatively charged free electrons. When the voltage between the electrodes reaches a certain level, the number of ions and electrons in the gas increases like an avalanche, causing the air to lose its insulating properties. This creates a discharge channel between the gap, resulting in a "breakdown" phenomenon. At this point, the gas forms a luminous body known as a "spark." Along with the heat and expansion, a "crackling" sound is also produced. The temperature of this electric spark can reach as high as 2,000 to 3,000°C, which is sufficient to ignite the air-fuel mixture in the engine's combustion chamber.
