What are the situations where spark plugs must be replaced?

[LilaDella]

There are several situations where spark plugs must be replaced: 1. Obvious stuttering sensation during cold starts; 2. Severe shaking when idling; 3. No spark or weak spark during grounding ignition test after removing the spark plug; 4. Oil stains on the spark plug; 5. Severe burning marks on the spark plug surface. The functions of spark plugs are: 1. To introduce the high-voltage electricity generated by the ignition coil into the engine cylinder; 2. To generate sparks between the electrodes of the spark plug to ignite the air-fuel mixture, ensuring normal engine operation. The working principle of spark plugs is: The electrode repeatedly and continuously generates electricity for ignition, producing pulsed high-voltage electricity that breaks down the air between the two electrodes of the spark plug, forming sparks and causing an explosion to ignite the air-fuel mixture in the cylinder, thereby starting the engine.