What are the common faults of car spark plugs?

[AaronFitz]

Common reasons for spark plug failure include the following: Incorrect spark plug gap adjustment. If the gap is too small, it not only limits the contact area between the spark and the air-fuel mixture but also suppresses flame kernel growth due to the flame-quenching effect of the electrodes. Although a spark occurs, it is weak, making it difficult to ignite the mixture. If the gap is too large, the ignition voltage provided by the ignition system may be insufficient to create a spark between the electrodes. Cracked spark plug skirt. High-voltage current leaks through the crack, preventing a spark at the electrodes. Electrode carbon buildup. The center electrode leaks current to the surroundings instead of sparking to the side electrode. Excessive carbon buildup on the spark plug can cause a short circuit, preventing sparking and potentially burning out the insulator, damaging the spark plug. Electrode damage. Prolonged electrical erosion from sparks or chemical corrosion from combustion gases can cause the electrode to break or detach, preventing sparking. Low insulation resistance of the spark plug. This reduces the ignition voltage applied to the spark gap, weakening the spark or even causing a complete loss of ignition function. Short circuit in the high-voltage wire. If the high-voltage ignition wire from the ignition coil to the distributor leaks, the entire engine may fail to start. If the wire from the distributor to the spark plug leaks, the spark plug in one cylinder may not fire. Burnt or eroded platinum contacts. This can cause all spark plugs to fail, preventing the engine from starting or running normally. Symptoms of spark plug failure include: Difficulty starting the car, whether cold or hot, often requiring multiple attempts. Engine shaking during driving. Reduced power, with noticeably weaker performance than usual. Increased fuel consumption. Stalling. Failed emissions tests. Faulty spark plugs should be replaced promptly. The replacement steps are as follows: Open the hood, remove the engine's plastic cover, and disconnect the high-voltage wires, marking each cylinder's position to avoid confusion. Use a spark plug socket to remove the spark plugs one by one, ensuring no leaves, dust, or debris are present and cleaning if necessary. Insert the new spark plug into the hole, hand-tighten it a few turns, then use the socket to fully tighten. Reinstall the high-voltage wires in the correct firing order and replace the cover. Spark plug replacement interval: Typically, spark plugs should be replaced every 40,000–60,000 km under normal maintenance conditions, but this may vary by brand and engine. Refer to the owner's manual for specific recommendations.