How to Determine Whether a Car Spark Plug is Good or Bad?
2 Answers
Methods to determine whether a car spark plug is good or bad are as follows: If the insulator appears tan, brown, or grayish-white, and the spark plug electrodes show minimal wear, the spark plug is in good condition and can be used for a longer period. If the spark plug is covered with black deposits, which may cause engine stalling in severe cases, it indicates carbon deposits and requires timely replacement. The functions of a spark plug are: 1. To introduce the high voltage electricity generated by the ignition coil into the engine cylinder; 2. To generate sparks between the spark plug electrodes to ignite the air-fuel mixture, ensuring the engine operates normally. Precautions for removing spark plugs: 1. Clean any dust or debris around the spark plug area using compressed air or a soft tube for blowing; 2. Ensure the engine is in a cold state before proceeding; 3. Immediately protect the spark plug hole after removal to prevent any debris or dust from entering the cylinder; 4. Avoid damaging the insulator ceramic body when using a wrench; 5. Do not bend or strike the center electrode when adjusting the spark plug gap.
My old car had been struggling to start, idling roughly, and fuel consumption kept climbing, so I suspected the spark plugs were failing. When I pulled them out, I found a layer of black carbon buildup around the electrodes. Measuring the gap with a tool, the standard 0.8mm had widened to nearly 1mm, indicating poor ignition. I then tried starting the car in the garage to observe the spark intensity—it was weak, not the usual bright blue flash. After promptly replacing them with new copper-core spark plugs, the car ran much smoother, with stronger acceleration and fuel efficiency restored. Spark plugs typically need inspection or replacement around 30,000 km. Neglecting them can cause engine misfires, affecting performance and longevity, so I’ve learned to maintain them regularly to avoid costly repairs. Remember to choose the right type and material—like iridium for durability—but basic checks are simple enough for anyone to do.
