How to Test the Condition of an Ignition Coil
2 Answers
Methods for testing the condition of an ignition coil: Turn on the ignition switch, confirm that the low-voltage circuit is functioning properly, then pull out the high-voltage wire from the center of the distributor cap, positioning it 3 to 5 millimeters away from the engine block. Use a screwdriver to repeatedly open and close the breaker points. If a blue-white spark jumps between the high-voltage wire and the engine block accompanied by a crisp sound, it indicates that the ignition coil is in good condition. If there is no spark and the high-voltage wire is confirmed to be functioning properly, it suggests that the ignition coil has failed. During engine operation, the condition of the ignition coil can also be judged by temperature: a slightly warm coil is in good condition, while a scalding hot one indicates a faulty or damaged ignition coil. Additionally, installing the suspected ignition coil on a gasoline engine with a fully functional ignition system for a spark test can also help determine its condition.
I usually judge the condition of an ignition coil by measuring its resistance. Using a multimeter, the primary coil resistance should be between 0.4 to 2 ohms, while the secondary coil should read between 5,000 to 15,000 ohms. If the readings fall outside these ranges, it indicates a faulty coil. During actual operation, I remove the coil for close inspection, checking for cracks or signs of electrical leakage on the housing, with special attention to any corrosion at the high-voltage output terminal. A spark test can also be performed by connecting the coil to a spark plug and grounding it while starting the engine – under normal conditions, a bright blue spark should be visible. These tests are best conducted when the engine is cold for more accurate measurement results. If abnormal operation is detected in a specific cylinder, the corresponding ignition coil should be prioritized for inspection.
