What are the symptoms of faulty spark plugs in a car?
2 Answers
Faulty spark plugs exhibit the following symptoms: Difficulty in starting the car, both cold starts and warm starts are challenging, often requiring multiple attempts. Engine shaking occurs while driving. Reduced power output, noticeably weaker than usual. Increased fuel consumption. Engine stalling. Failed exhaust emissions. Common causes and diagnosis of spark plug failures: Several common issues can cause spark plugs to malfunction: Incorrect spark plug gap adjustment. A gap that's too small limits the contact area between the spark and the air-fuel mixture and suppresses flame kernel growth due to the electrode's flame-quenching effect. Although sparking occurs, the spark is weak, making it difficult to ignite the mixture. Conversely, a gap that's too large may prevent sparking if the ignition system cannot provide sufficient voltage. Cracked spark plug skirt. High-voltage current leaks through the crack, preventing sparking at the electrodes. Electrode carbon buildup, causing the center electrode to leak current to the surroundings instead of sparking to the side electrode. Excessive carbon deposits can short-circuit the spark plug, preventing sparking and potentially damaging the insulator. Electrode damage. Prolonged electrical erosion from sparks or chemical corrosion from combustion gases can cause electrodes to break or detach, preventing sparking. Low insulation resistance of the spark plug. This reduces the ignition voltage applied to the spark gap, weakening or completely eliminating the spark. Short circuit in high-voltage wires. 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, the spark plug in that cylinder may not spark. Eroded platinum contacts. This can cause all spark plugs to fail to spark, preventing the engine from starting or running normally. Faulty spark plugs should be replaced promptly. The replacement steps are as follows: Open the hood and remove the engine's plastic 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 external debris like leaves or dust and clean thoroughly. Place the new spark plug into the spark plug hole, hand-tighten it a few turns, then use the socket to tighten it fully. 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 kilometers under normal maintenance conditions. However, this may vary depending on the brand and engine type. Always refer to the owner's manual for specific recommendations.
I noticed that when the spark plugs have issues, the engine becomes very uncooperative. Starting the car is particularly difficult, especially on cold mornings—it takes several turns of the key to get it going. Once on the road, the car idles roughly, shaking so much that the steering wheel vibrates, making it feel like sitting in a massage chair. Acceleration is noticeably slower, struggling on inclines, and even flooring the pedal doesn’t quickly raise the RPM. Fuel consumption spikes, burning through a full tank in just over a week, thinning out the wallet. Additionally, black smoke from the exhaust and a strong gasoline smell indicate incomplete combustion. Sometimes, knocking or popping sounds can be heard—all signs of worn spark plugs. It’s best to inspect or replace them on schedule, typically around 50,000 kilometers, to avoid unexpected breakdowns. You can also check them yourself: pull them out to see if the electrodes are fouled or eroded.
