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Gasoline engines require three ingredients to create combustion — spark, fuel, and compression. If any of these three isn’t present, you’ll have a misfiring or dead car on your hands. The ignition coil, along with spark plugs, is the key element that ensures spark in gasoline engines.
When the ignition coil goes bad, it can completely disrupt your motor or even prevent it from running altogether. Join us as we go over the most common causes and symptoms of ignition coil failure!
Article updated on 12/16/21. Original publishing date 03/16/21
What Is an Ignition Coil?
To better understand ignition coil failure causes and symptoms, one must have a basic understanding of the purpose of an ignition coil and how it works. While an ignition coil has evolved over the years, its purpose, which is to boost voltage, hasn’t changed. A car’s battery voltage that’s usually about 12V just isn’t sufficient for combustion, but with an ignition coil, it’s converted or transformed into the thousands of volts needed.
As for how it works, simply put it is an electromagnetic induction device or inductor that uses two-wire coils in which lower voltage direct current is fed through the primary coil to generate higher voltage spark pulses in the secondary coil.
Most Common Ignition Coil Failure Causes
As mentioned before, ignition coils have evolved over the years and the most modern one is the coil on plug system. It’s also the most relevant and widely used type of ignition coil, and for that reason, this guide is based around it.
That being said, it still shares the same basic principles as the other types of ignition coils, thereby sharing many failure causes and symptoms.
High Heat
One of the most common ignition coil failure causes is a high amount of heat. While the coils are made from a silicon-iron alloy that has a tolerance to high temperatures, the same can’t be said about the rest of the materials used.
Yes, they can handle the heat, but it’s either super high temperatures or multiple heat cycles over an extended period that can cause them to deteriorate.
Spark Plug Issues
Since spark plugs work so closely with ignition coils, a problem with them can directly affect the performance of ignition coils. Ignition coil failure can occur due to a worn-out spark plug because it forces the coil to overcompensate and work at a much higher output. This, in turn, causes additional wear on the ignition coil and could lead to voltage overload and overheating.
Another ignition coil failure cause is when a spark plug has an improper plug gap. An excessive gap will result in ignition overwork, just like it would with a worn-out plug. When an ignition coil is under such added strain for an extended period, it’s highly likely to fail.
Vibrations
Despite being built to withstand a significant amount of vibrations, excessive ones caused by other issues with the engine can damage ignition coil windings and even the surrounding insulation, which can lead to malfunctioning or failure.
Moisture
Moisture is yet another cause of ignition coil failure. It has been noticed the seal situated between the valve cover and the ignition coil can fail over time. Consequently, moisture can make its way around the spark plug and ignition coil causing unwanted oxidation and corrosion.
That’s not all, if your car is also suffering from a leaky valve cover gasket, which is quite common, there’s a high possibility of oil making its way into the gap thereby causing ignition coil failure.
Connector Pin Issues
While it’s not as common as other causes listed above, there’s a possibility of something going wrong with the connector pin.
These ignition coil pins also undergo heat cycles and vibrations and can end up breaking or corroding. Degreasers and water could also make their way inside the connector, and compromise the pins.
How to Spot a Bad Ignition Coil?
Now that you know what causes ignition coil failure, here are the most notable symptoms to look out for. However, as car components are so interconnected, these symptoms don’t necessarily mean a bad ignition coil. Any of these could be caused by something entirely different. For example, a no start condition can be caused by a bad ignition coil but also a failing fuel pump that isn’t feeding enough fuel to the engine. That being said, these are a good indicator that something’s up with your coils.
Backfires
A car backfires when unburnt fuel makes its way out of the combustion chamber and ignites in either the exhaust or intake manifold. While this was a more common occurrence on older vehicles, it’s quite rare to see it on modern cars as fuel and spark delivery is managed with exact precision thanks to advanced electronics. This makes a backfire on a modern vehicle even more concerning.
A backfire is considered to be one of the earliest symptoms of ignition coil failure. And it’s also advisable to get it fixed soon as it could damage the pricey catalytic converter that’s part of your exhaust system.
Poor Fuel Economy
With unburnt fuel-burning where it shouldn’t and causing backfires, it shouldn’t be a surprise then that ignition coil failure can affect fuel economy. However, it’s not only the backfiring that’ll reduce your MPG.
When the insufficient voltage reaches the spark plugs, your engine starts to use more fuel to compensate. This fuel is wasted and can even make its way out of the exhaust in the form of vapor without causing backfires. This is why it’s always a good idea to have a rough understanding of your car’s fuel economy numbers.
Trouble Starting
If you are facing trouble starting your car despite having both battery leads securely connected and a fully charged battery, it’s a telltale sign of ignition coil failure. A bad coil would send insufficient power to a spark plug, which in turn would make starting the car more difficult. Check battery terminals for corrosion. If you spot any, first clean the terminals and give it another try. If the issue persists, the ignition coils could be the culprit.
Misfiring Motor
Like backfires, engine misfires are a serious issue in modern engines. Ignition coil failure will often lead to regular misfires in one or more cylinders. Along with the unpleasant noises, you will also notice your engine bogging down, especially during acceleration. Another clear indication is unusual vibrations at idle.
Vehicle Stalling
Don’t be surprised if your car begins stalling, as it’s an expected byproduct of ignition coil failure.
This occurs because your car is having trouble creating spark. If the spark gets irregular, it’ll even have trouble starting after it stalls.
Check Engine Light
Lastly, most modern cars have an error code specific to ignition coil malfunction. The car will alert you via the check engine light and a scan tool should give you the information. If you are quick to respond to the warning light, it might just save you from dealing with the more serious symptoms mentioned above.
How to Diagnose a Bad Ignition Coil?
The best way to diagnose a bad ignition coil is to take the suspect one and have it swap places with a working one. You’ll first need to identify which cylinder is the cause of the issue, which can often be done by unplugging individual ignition coil leads while the engine is working, If you notice a change in sound once you kill power to an ignition coil, chances are that it’s good. Once you unplug an ignition coil and the engine maintains the same note, you’ve located your faulty coil.
Can You Drive a Car With a Bad Ignition Coil?
Despite having a hugely important role in keeping your car running, you could drive the car for a few miles if you were early to detect an ignition coil failure. If your car isn’t showing any of the major symptoms like jerking and stalling, it would be the best time to drive it straight to the workshop or your garage.
That being said, it would be highly irresponsible to ignore the problem till it gets worse as you’re running a risk of damaging your engine to a point of failure. In most vehicles, ignition coils are fairly easy to replace, which is a further reason to not delay getting them sorted out!
Don’t Wait Until It’s Too Late!
While ignition coils have a long service life, they can reduce drastically if the car hasn’t been maintained well. Ignition coils should be swapped out if you have lost track of when they were last replaced. If your car is equipped with a coil-on plug system, we’d recommend swapping out the entire set to get the most out of them. Head over to our Shop and find quality OEM ignition coils to make sure your car is getting the spark it needs!
