A vehicle’s ignition system must provide enough sparks to the correct cylinder every minute at the correct time. It is absolutely necessary to perform accurate ignition maintenance. With the help of our best practice guide for repairing ignition coils, you will understand how they work, why and how they fail, and how to replace them to obtain high-quality, long-lasting repairs that you and your customers can trust.
Why do ignition coils fail?
Although the design of ignition coils is durable, the increasing demand for them means that they may fail.
Damaged spark plugs or plug wires: Excessive resistance of the damaged spark plug or spark plug wire will cause the output voltage of the coil to increase-if it exceeds 35,000 volts, it may damage the internal insulation of the coil and cause a short circuit. This will result in a decrease in output, leading to misfires and/or poor starting under load.
Worn or excessive spark plug gap: As the spark plug wears, the gap between its two electrodes will also wear, which means that the coil must now generate a higher voltage to bridge it. The increased strain on the coil can cause voltage overload, which in turn can lead to overheating.
Vibration damage: The continuous wear and tear caused by engine vibration can damage the ignition coil winding and insulation, resulting in short-circuit or breakage of the secondary winding. Similarly, it can loosen the electrical connection at the spark plug, forcing the coil to work overtime to ignite the spark plug.
Overheating: Due to their location, ignition coils are often exposed to excessive engine temperatures. This will reduce the conductivity of the coil and affect the ignition coil's performance and life.
Varying resistance: A short circuit or low resistance in the coil winding will increase the current through the coil, which can damage the entire ignition system. The change in resistance may also cause faint sparks, which may cause the vehicle to fail to start and damage the ignition coil and surrounding components.
Excessive moisture: The most likely cause is oil leakage when the valve cover gasket fails, causing oil to accumulate around and damaging the ignition coil and spark plug. For example, water from A/C condensation can also penetrate into the system. In both cases, it is important to address the root cause to avoid repeated failures.
What are the symptoms of a faulty ignition coil?
Since the ignition coil is responsible for generating the engine spark that starts the vehicle, any problems will quickly manifest in engine performance issues, such as:
Check engine light on: because faulty ignition coil directly affects engine performance, any problem will trigger check engine light.
Poor fuel economy: The less spark energy, the lower the efficiency of the combustion process, resulting in a significant drop in fuel economy.
Vehicle backfiring: It is usually an early symptom of ignition coil failure, which occurs when any unused fuel in the combustion chamber is discharged through the exhaust system. If left unchecked, this can cause significant and costly damage to the exhaust.
Vehicle stalling: A broken ignition coil will deliver irregular current to the spark plug, causing the vehicle to stall. This may eventually prevent the vehicle from starting to reverse.
Engine misfire: Because one or more engine cylinders do not provide enough power for the vehicle, the engine will misfire, especially during acceleration.
Problems starting the vehicle: Similarly, if one or more spark plugs do not receive enough power, it will cause problems when starting. In a car with a single-coil, this means that the car cannot start at all.
How to troubleshoot an ignition coil？
If you suspect a problem with the ignition coil, simply follow the steps below to simplify your diagnosis:
Use diagnostic tools to read any fault codes and real-time data. Compare the value of the suspected faulty coil with the value of the normal working coil.
Inspect the coil for any signs of damage, such as cracks in the housing, breakage of the anti-rotation sheet, or damaged wires or plug connections.
In addition, remove and inspect the spark plug. Check the spark gap and plug wires (if applicable) to ensure that the resistance of the wires is within specifications.
Turn on the ignition switch and use a multimeter to measure the supply voltage of the ignition coil. Voltages exceeding 10.5V should be recorded.
Use the multimeter again to check the primary and secondary circuits of the coil. The primary resistance of most coils should be between 0.4 and 2 ohms, and the secondary resistance should be between 5,000 and 20,000 ohms, but please refer to the vehicle manufacturer's specifications. If one of them does not meet the specifications, replace it. A zero reading indicates that the coil is short-circuited, and a high reading indicates that the coil is open. If the ignition coil has 3, 4, 5, or 7 wires, please refer to the wiring diagram showing the electrical design of the internal coil.
How to replace an ignition coil？
After confirming the fault, follow the simple steps below to replace the coil:
Turn off the ignition of the vehicle and find out the faulty coil. Unplug the electrical connector, and then unscrew the bolts that hold it in place. You should now be able to carefully remove the coil from its mount.
Before installing the new ignition coil, it is best to apply insulating grease on the bottom of the new coil and its power socket. This will prevent corrosion and ensure a good connection. It is also recommended that you replace all spark plugs at the same time you replace the coil.
Now slide the new coil into its housing. Tighten the bolt to the recommended torque, and then reconnect the electronic connector.
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Carry out a road test to ensure everything is in good working order.
