How to Determine if an Ignition Coil is Good or Bad?
2 Answers
Methods to determine if an ignition coil is good or bad include: 1. Touch the outer shell of the ignition coil to sense its temperature—feeling warm is normal, while feeling scalding hot indicates a short circuit between turns in the ignition coil; 2. Use a multimeter to measure the resistance of the primary and secondary windings. If the resistance is infinite, it indicates an open circuit fault in the winding. If the resistance is too high or too low, it suggests poor contact or a short circuit between turns in the winding. The working principle of an ignition coil is: it repeatedly stores and releases energy at different frequencies according to the engine's varying speeds. When the primary coil is connected to the power source, a magnetic field is generated around it as the current increases, and the iron core stores the magnetic field energy. When the switching device disconnects the primary coil circuit, the magnetic field of the primary coil rapidly decays, inducing a high voltage in the secondary coil.
To determine the health of an ignition coil, I typically start with observable vehicle symptoms. For instance, difficulty starting the engine or jerking during acceleration may indicate insufficient spark production by the coil. When parked, pop the hood and feel the coil's surface temperature—if it's scalding hot or shows visible cracks/burn marks, there's likely an issue. The simplest test is removing a spark plug wire and performing a spark test; strong blue sparks are good, while weak or absent sparks signal trouble. For precision, use a multimeter to measure resistance—normal range is 5,000 to 15,000 ohms, deviations indicate failure. Always disconnect the battery before coil replacement to prevent shocks. Monitor for sudden fuel consumption spikes or black exhaust smoke while driving—these are early warnings that prompt attention can save significant repair costs.
