8 Symptoms of a Bad Ignition Coil
Your vehicle’s ignition coils provide electrical current to the spark plugs to make combustion possible. But a bad coil can cause misfires, poor performance, and unburned fuel. Ignoring a faulty ignition coil can increase the problem and damage your catalytic converter, resulting in additional costs.
Read on to learn about the most common symptoms of a bad ignition coil and the average replacement cost.
How an ignition coil works
Ignition coils are known as small electrical transformers. Its purpose is to convert the low 12 volt current typically found in a car battery into the much higher voltage required to ignite the fuel and start the engine.
Each spark plug in your car has its own ignition coil. The coil is either physically connected to the spark plug with a wire or placed on the spark plug without a wire.
A spark plug requires approximately 15,000 to 20,000 volts of electricity to form an electric spark that can ignite the fuel. Without a strong ignition coil, you may experience poor fuel economy or engine misfires. It is important to note that a faulty ignition coil can also be related to low or abnormally high battery voltage. This can cause many other car issues as well, and upgrading to a new battery can solve many of them.
Many batteries in older cars can simply fail over time, and one of the signs that your battery is bad is that it doesn’t show at least 12.65 volts when fully charged. That way, you’ll know there’s a problem with your battery.
Symptoms of a faulty ignition coil
If your ignition coil is starting to fail, your car will give you some clues. These symptoms can range from subtle performance issues to more obvious issues that affect your drivability. Identifying these signs early can help prevent more serious engine damage and costly repairs.
1) Engine Misfires
Engine misfires are often the first and most noticeable sign of a bad ignition coil. When you start your car, you may hear a sputtering or coughing noise. This is an indication that one or more cylinders are not firing properly.
When driving around town, you may notice jerking, hesitation, and loss of power, especially when accelerating. The engine may vibrate more than normal or run rough when idling. These problems occur because a defective coil does not provide enough voltage to the spark plug, causing incomplete combustion in one or more cylinders.
2) Check Engine Light Illuminated/DTC Codes
One of the most reliable indicators of many problems in modern cars (including ignition coil problems) is the Check Engine Light (CEL) illuminated on the dashboard. This warning is often accompanied by an error code stored in the vehicle’s computer system.
Scanning for error codes is probably the easiest way to troubleshoot a coil problem, so if you see this CEL, get a diagnostic tool or have a repair shop check it for you.
3) Poor fuel economy
Another common sign of a faulty ignition coil is reduced fuel consumption. If the ignition coil doesn’t function properly, the fuel in the engine cylinders can burn incompletely. As a result, your vehicle may use more fuel than usual to keep up with performance.
You may (if you’re careful) notice that you have to fill up your gas tank more often or that your fuel economy drops. This increased fuel consumption occurs because your engine has to work harder to compensate for the misfire caused by a faulty ignition coil.
4) Engine Stalling
Failed ignition coils can also cause your vehicle to stall. This can be caused by the irregular spark that the defective coil sends to the spark plugs. Your car may shut down completely when it comes to a stop and struggle to start again.
Engine stalling can be a more serious symptom of a faulty ignition coil. This occurs when the defective coil can’t produce the spark needed to keep the engine running. Your car may suddenly stall while waiting at a traffic light or driving slowly.
Leaving the car running is particularly dangerous as it may leave you powerless or at risk of a road accident. Engine stalls due to ignition coil problems are often intermittent at first and become more frequent as the problem worsens.
5) Difficulty starting the engine
A defective ignition coil can make your vehicle difficult to start, especially in cold weather. When you turn the key or press the start button, you may notice that your engine takes a long time to start or that it takes multiple tries before it finally starts.
This is because the weak spark caused by a defective ignition coil makes it difficult to ignite the mixture in the combustion chamber. This problem is more noticeable in cold weather, when the engine oil thickens and requires more energy to start.
If you have to crank your engine longer than usual, especially on cold mornings, or if your engine doesn’t start on the first try, it could be a sign of a bad ignition coil.
6) Backfiring
If your vehicle backfires at times, you may have an ignition coil problem on your hands. Backfiring occurs when unburned fuel enters the exhaust system and ignites there instead of in the combustion chamber.
You might hear a loud “pop” or “bang” coming from the exhaust pipe, sometimes accompanied by a puff of black smoke and/or a fuel smell. In some cases, you may literally see flames shooting from the exhaust. This symptom not only affects your vehicle’s performance and makes it annoying loud, but can also damage the exhaust system if you ignore it.
7) Rough idling
A faulty ignition coil often makes itself known as rough idling when your vehicle is stationary. When you’re stopped at a traffic light or parked with the engine running, you might notice unusual vibrations or a shaky feeling throughout the car.
The engine may sound uneven, with a choppy or unsteady rhythm instead of a smooth purr. You might also observe fluctuations in the RPM gauge, with the needle wavering more than usual.
This rough idling occurs because the failing ignition coil isn’t providing consistent spark to one or more cylinders, causing the engine to run unevenly. If your car starts to feel more like a massage chair than a smooth-running machine when idling, it’s worth checking the ignition coils.
8) Poor Power and Performance
During acceleration, the car might feel sluggish or unresponsive, struggling to gain speed when you press the gas pedal. You may notice hesitation or jerking, especially when trying to climb a hill or merge onto a highway.
At higher speeds, the engine might not maintain power consistently, leading to difficulties in passing other vehicles. Additionally, you could experience intermittent power loss, where the car briefly loses power and then regains it, creating a sporadic driving experience.
While experiencing these power-related problems doesn’t necessarily mean you have a bad ignition coil (there are many other causes), when you notice this symptom along with others above, the odds of a coil being at fault increase.