What Causes Spark Plug Misfire?
2 Answers
Common reasons for spark plug failure include the following: Incorrect spark plug gap adjustment. If the gap is too small, it not only limits the contact area between the spark and the air-fuel mixture but also suppresses the growth of the flame kernel due to the quenching effect of the electrodes. Even if a spark occurs, it will be weak, making it difficult to ignite the mixture. If the gap is too large, the ignition voltage provided by the ignition system may be insufficient to create a spark between the electrodes. Cracked spark plug skirt. High-voltage current can leak through the crack, preventing a spark from forming at the electrodes. Carbon buildup on the electrodes. The central electrode may leak current to the surroundings instead of jumping to the side electrode. Excessive carbon deposits can short-circuit the spark plug, preventing it from sparking and potentially damaging the insulator. Damaged electrodes. Prolonged electrical erosion from sparks or chemical corrosion from combustion gases can cause the electrodes to break or detach, rendering the spark plug unable to spark. Low insulation resistance of the spark plug. This reduces the ignition voltage applied to the spark gap, weakening the spark or completely disabling ignition. Short circuit in the high-voltage wire. If the high-voltage ignition wire from the ignition coil to the distributor leaks, the entire engine may fail to start. If the wire from the distributor to the spark plug leaks, one cylinder's spark plug may misfire. Burnt or eroded contact points. This can cause all spark plugs to misfire, preventing the engine from starting or running normally. Symptoms of spark plug failure include: Difficulty starting the car, both when cold and warm, often requiring multiple attempts. Engine shaking or vibration while driving. Reduced power, with noticeably weaker acceleration than usual. Increased fuel consumption. Engine stalling. Failed emissions tests. Faulty spark plugs should be replaced promptly. The replacement steps are as follows: Open the hood and remove the plastic engine cover. Disconnect the high-voltage wires, marking each cylinder's position to avoid confusion. Use a spark plug socket to remove the spark plugs one by one. Check for debris like leaves or dust and clean the area thoroughly. Insert the new spark plug into the hole, hand-tightening it a few turns before using the socket to secure it. Reinstall the high-voltage wires in the correct firing order and replace the cover. Spark plug replacement interval: Typically, spark plugs should be replaced every 40,000-60,000 km under normal maintenance conditions. However, this may vary depending on the brand and engine type, so consult the owner's manual for specific recommendations.
As a lifelong car enthusiast, I've encountered spark plug misfires countless times, mainly due to aging spark plugs with carbon buildup leading to poor insulation, or worn-out ignition coils with insufficient output. Loose or corroded wires and connectors can also interrupt the current, and engine computer errors sending wrong signals can trigger faults too. I remember once on a long trip when the car was shaking badly—stopping to check revealed the spark plugs were heavily carbon-fouled, and replacing them solved the issue. Regular maintenance is key: inspect and clean spark plug gaps every 20,000 km, and don’t wait until problems escalate. Cold starts often worsen the issue, so using antifreeze helps prevent it. Small money-saving habits can avoid major headaches—timely fixes protect engine longevity.
