How to Test Whether a Spark Plug is Good or Bad?

1 Answers
OElisa
07/29/25 2:39pm
Testing methods for spark plugs are as follows: 1. Unscrew the spark plug and place it on the cylinder block, then test for spark using a high-voltage wire. If there is no spark or the spark is weak, it indicates that the spark plug is leaking electricity or not working; 2. Let the engine idle and carefully listen for changes in engine speed and sound. If the changes in speed and sound are obvious, it indicates that the spark plug is normal. If the changes in speed and sound are not obvious, it indicates that the spark plug is in an abnormal state. 3. If the spark plug is severely eroded, with phenomena such as pitting, black streaks, cracks, or melted electrodes at the top, it indicates that the spark plug is damaged and must be replaced immediately; 4. If the spark plug is black as if smoked, it indicates that the cold/hot type of the spark plug is wrong or the air-fuel mixture is too rich, or engine oil is leaking. If the spark plug is reddish-brown or rust-colored, it indicates that the spark plug is normal.
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