How to Determine Whether a Car Spark Plug is Good or Bad?

[StNoah]

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.

[LaStephanie]

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.

[LaJohnny]

As a car repair enthusiast who often tinkers with car parts myself, the key steps to judge the quality of spark plugs involve visual inspection and testing. First, pull out the spark plug and examine it: a normal electrode should be grayish-brown, clean, and free of cracks. If there's excessive carbon buildup or the electrode is eroded or deformed, it's faulty. Next, use a gap gauge to measure the standard gap of around 0.8mm—adjust or replace it if it doesn't meet the specification to save money. Then, test the spark strength with a simple method: ground a wire to the car and start the engine to observe the spark frequency; a strong spark indicates good condition. When replacing spark plugs, match the type—for example, nickel alloy plugs are cheaper but wear out faster, while iridium plugs last longer. Worn-out spark plugs can cause rough idling, poor acceleration, increased fuel consumption, and air pollution due to leaks. That's why I always check them during every 30,000-kilometer maintenance to prevent sudden failures, save money, and avoid wasting time and money at the repair shop.

[DiGiselle]

When I was a novice driver and encountered spark plug issues without knowing what to do, the mechanic taught me: faulty spark plugs make the car hard to start, cause rough idling, increased vibration, and higher fuel consumption. During inspection, pull them out to check—if the electrode color is off or there's carbon buildup, they need replacement; use a feeler gauge to adjust if the gap is too large. He demonstrated that a normal spark is bright blue, while a faulty one is dim red with weak sparks. Now I know to replace spark plugs every 25,000 kilometers to avoid major problems, ensuring safety, emission compliance, and cost savings.