How to Determine Whether to Replace Spark Plugs?
2 Answers
Methods to determine whether to replace spark plugs: 1. Misfire Test Method: Let the engine idle, and use a screwdriver to misfire the spark plug. If the misfired spark plug is faulty, the engine operation remains unchanged. If the engine shakes immediately after misfiring, it indicates that the cylinder is working normally. 2. Comparative Test: Swap the spark plugs between a well-functioning cylinder and a poorly functioning cylinder for a comparative test to further determine the quality of the spark plugs. 3. Spark Test: Remove the suspected faulty spark plug and place it flat on the engine block. Disconnect the high-voltage distributor wire and touch it to the spark plug terminal. Turn on the ignition switch and move the distributor points to make the high-voltage electricity jump between the spark plug electrodes. If the spark is continuous and bright, the spark plug is good. 4. Visual Inspection: Remove the spark plug and observe the electrode color. Spark plugs with white or rust-colored electrodes are working normally; those with black smoke (excluding factors of overly rich mixture) have poorer working quality; those with severe carbon deposits or oil stains have the worst working quality or cannot work at all.
To determine whether to replace the spark plugs, I always observe the engine's response. If the car has difficulty starting, such as requiring several attempts to ignite, or if the engine idles roughly and shakes, it's likely a spark plug issue. Lack of power during acceleration or a sudden increase in fuel consumption are also common signs. It's best to remove them and inspect the electrodes: if the gap has widened beyond 1mm, or if they appear blackened, oily, or severely carbon-fouled, it's time for new ones. Failing to replace them can damage the ignition coils, and delaying the replacement will cost more in the long run and compromise safety. I once experienced this—the engine kept stalling, but after changing the spark plugs, it ran much smoother immediately.
