What are the signs of a bad ignition coil?
3 Answers
Signs of a bad ignition coil: 1. During idle, the vehicle body shakes noticeably, and the exhaust pipe vibrates severely, making a "popping" sound; 2. While driving, when the engine speed is below 2500 rpm, the vehicle body shakes noticeably with poor acceleration, but the shaking sensation disappears when the speed exceeds 2500 rpm; 3. Upon opening the engine hood, the engine is observed to shake significantly with a large amplitude. The ignition coil is a transformer whose initial energy comes from the battery's 12V voltage, but the energy delivered to the spark plug can reach tens of thousands of volts. It is through the energy conversion of the ignition coil that the spark plug can generate immense energy, allowing the air-fuel mixture in the engine cylinder to combust.
I often drive long distances and have noticed several warning signs before an ignition coil fails. The engine shakes violently, especially when accelerating, causing the car to jerk and feel like it's losing power. There's a sudden significant increase in fuel consumption—it feels like the gas disappears quickly even after refueling. Cold starts become difficult, with the car coughing a few times before firing up. Sometimes, black smoke comes out of the exhaust with a pungent smell. The ignition coil is responsible for delivering high-voltage electricity to the spark plugs. Once the insulation ages or an internal break occurs, the spark plugs fail to ignite, causing uneven cylinder operation. My car had this issue last time—it shook so badly that the steering wheel vibrated in my hands, and the check engine light came on, prompting me to get it fixed immediately. Delaying repairs can also damage the catalytic converter, leading to higher repair costs. During regular maintenance, ask the technician to test the coil's resistance and check insulation with a multimeter to prevent problems. Be extra cautious during heavy rain, as moisture can easily cause coil failure. Replacing the coil promptly saves money and ensures safety.
I've been repairing cars myself for several years, and it's quite easy to recognize the signs when an ignition coil is failing. The symptoms include the engine shaking like a washing machine while driving, noticeably sluggish acceleration, and the fuel gauge dropping rapidly. You'll also experience increased instances of failed starts, along with abnormal and noisy ignition sounds. Plugging in an OBD scanner to read the trouble codes will confirm an ignition issue if P0300 series codes appear. If you check the car at night and see blue sparks leaking from the exposed part of the coil, that's another clear sign. I've used a multimeter to measure the coil's resistance—if it deviates significantly from the specified value, it's time for a replacement. Regularly inspect the spark plugs for carbon buildup; black marks indicate ignition failures. Testing under hot conditions is more accurate since coils are prone to failure when heated. Replace the faulty coil early with a reputable brand to avoid towing hassles and extra costs. Make it a habit to check your engine's condition for peace of mind during high-speed driving.
