How to Determine if an Ignition Coil is Good or Bad?
4 Answers
Methods to determine the condition of an ignition coil: Check by turning off the ignition switch, disassembling the ignition coil assembly, and using a multimeter to measure the resistance of the secondary coil, which should be between 7.0~9.5kΩ. If the resistance is incorrect, the ignition coil needs to be replaced. Here are situations indicating a damaged ignition coil: 1. Individual cylinders not working without spark, leading to rough idling and lack of power when accelerating. If the ignition coil is leaking electricity, the engine may or may not shake at idle, but it will definitely shake and lack power when accelerating. 2. Improper use of the ignition coil can cause damage. Therefore, care should be taken to prevent the ignition coil from overheating or getting damp. Do not turn on the ignition switch when the engine is not running. Regularly inspect, clean, and tighten wiring connections to avoid short circuits or grounding. Control engine performance.
A while ago, my car kept jerking when refueling, and after inspection, it turned out to be an issue with the ignition coil. Here are some practical tips: First, start the engine and unplug each ignition coil connector one by one while listening for changes in engine sound. If unplugging a certain coil doesn’t affect the RPM, that coil is likely faulty. Also, observe whether the car shakes during cold starts or if there’s jerking during acceleration—these symptoms often point to a coil problem. A sudden increase in fuel consumption is another red flag. If possible, measure the coil’s resistance; it should normally be between 0.4 to 2 ohms. If it exceeds this range, replacement is necessary. Don’t delay—ignoring a faulty coil can severely damage the catalytic converter. If you’re unsure, take it to a repair shop and let a mechanic diagnose it with professional equipment.
A faulty ignition coil does more than just increase fuel consumption. I've experienced situations where it took three or four attempts to start the engine when cold, sudden misfires and loss of power during highway driving, and the annoying flashing of the engine warning light on the dashboard. Here's a simple trick: keep a flashlight handy to inspect the coil housing—if you spot cracks or signs of melting, that's a sure sign of trouble. The easiest test is to swap the suspected bad coil with a known good one; if the problem moves with the coil, it's time for a replacement. Don't forget to check for poor connector contact, which can cause similar symptoms. If you smell burning, stop the car immediately and address the issue.
Three tricks to diagnose ignition coils. First, check the engine fault codes - the misfire data stream won't lie. Second, use a multimeter to measure secondary winding resistance, typically 5k-15kΩ is normal. Third, pay special attention to aging and leakage marks, especially cracked insulation boots during humid seasons which are most critical. Remember to regularly clean oil sludge around spark plugs as these contaminants can cause coil overheating. DIY replacement isn't difficult - just follow the service manual for plugging/unplugging, but make sure to align the clip positions properly.
