What are the symptoms of faulty car spark plugs?
3 Answers
The symptoms of faulty car spark plugs include: 1. Electrodes becoming rounded and insulators developing scars; 2. Causing the engine to produce excessive carbon deposits; 3. Electrodes melting and insulators turning white; 4. Difficulty in starting the car; 5. Black smoke from the exhaust pipe; 6. Rough idling; 7. Excessive exhaust emissions; 8. Insufficient power. Car spark plugs are categorized into: 1. Standard spark plugs: The insulator skirt slightly recedes into the shell end face, with the side electrode outside the shell end face; 2. Insulator-protruding spark plugs: The insulator skirt is longer, protruding beyond the shell end face; 3. Fine-electrode spark plugs: The electrodes are thin, characterized by strong sparks and better ignition capability.
In my experience, when spark plugs go bad, your car will give you plenty of obvious warning signs. Starting the engine becomes unusually difficult—you might have to turn the key multiple times before it fires up, accompanied by a sputtering sound, as if the engine is protesting. At idle, it's even more noticeable: the engine shakes like a seismograph, vibrating the steering wheel so much it numbs your hands—a distinctly unsettling feeling. When driving, you'll notice a lack of power; pressing the accelerator feels like a snail crawling, making overtaking or climbing hills a struggle. Fuel consumption also inexplicably spikes—what used to be an easy 500–600 km per tank suddenly drops to 400–500 km before the low-fuel light comes on, wasting money and increasing pollution. In severe cases, you might see black smoke from the exhaust or smell burning, indicating incomplete combustion. Ignoring it long-term can damage core engine components, so I recommend checking your spark plugs every 20,000 km. Replacing them early ensures smoother performance, better fuel efficiency, and peace of mind—a habit that keeps your car running strong.
I learned my lesson with my old car due to faulty spark plugs. At first, starting was extremely difficult—it took three attempts to fire up the engine in cold winter mornings, making a choking sound. Later, the idle became terribly unstable; at red lights, the whole cabin would shake, vibrating the seats so much my back went numb. Friends joked it was like driving in a massage chair. Acceleration suffered too—stepping on the gas yielded no response, making highway overtaking risky with fear of rear-end collisions. The biggest pain was the soaring fuel consumption: city driving went from 8L/100km to around 10L, hurting my wallet. The exhaust even carried a sulfur smell, polluting the air and making it unpleasant to roll down windows. A later garage visit revealed severe carbon buildup on the spark plugs. After replacement, everything ran like new. The takeaway? Don’t ignore small warning signs—timely checks can prevent major repairs.
