What are the symptoms of a bad spark plug?

1. The insulator skirt, electrodes, and casing are covered with a dark compound; 2. The engine power becomes dull when driving; 3. Fireworks or black smoke are emitted during exhaust; 4. The vehicle vibrates at idle speed and is difficult to start; 5. Exhaust The inside of the tube turns black, accompanied by the discharge of raw oil; 6. The engine shakes regularly. The reasons for a broken spark plug are: 1. The spark energy is small during flashover; 2. The air-fuel ratio of the fuel mixture is large; 3. The engine runs overheated; 4. The air filter is too dirty; 5. The speed is too high at idle; 6. , Serious carbon deposits and the use of inferior gasoline; 7. Damage to the valve oil seal or damage to the crankcase ventilation valve.