The ignition coil is a part of most cars with petrol engines. Usually, a car has more than one of these coils, with each one connected to a different cylinder in the engine. Its job is to provide the engine with the strong electrical jolts needed to make the fuel burn correctly. This might seem like a small thing, but it’s really important for how well your car uses fuel and how reliable it is. Like other important parts, these coils need to be checked and taken care of regularly.
Petrol cars usually run on a 12-volt battery. This battery can start the engine by powering a starter motor, but it’s not powerful enough to make the fuel burn. (For that, you need a spark plug, which needs much more voltage, about 40,000 volts.) That’s where the ignition coil comes in. It has a special part called a transformer that boosts the voltage from the battery into quick bursts of thousands of volts. These bursts of electricity are sent to each spark plug at exactly the right time during the engine’s cycles, making the fuel burn and creating power. Diesel engines don’t have ignition coils because they don’t need them; they make the fuel burn using only heat and pressure.
A modern ignition coil looks like a rubber cap that fits onto a spark plug. On top, there’s a connector for electricity and some threads to attach it securely to the engine. Inside, there’s a bunch of tightly wound copper wire that makes up the transformer. This wire is wrapped around an iron core that becomes a magnet when electricity flows through it. The energy from this magnetic field is what gets sent to the spark plug. The whole thing is surrounded by a special material to stop electricity from leaking out and causing problems. The ignition coil works by using a scientific law called Faraday’s law of induction to create a lot of power. This same law is used to make electric motors and generators too.
In the early days, cars had just one ignition coil packed into a part called the distributor. This distributor sent electricity to each spark plug, making sure the fuel burned at the right time. But over time, the distributor could get out of sync, causing engine problems. Around the 1980s, car companies started using electronic sensors to control when the fuel ignited, and they started using multiple ignition coils for more power and efficiency. Nowadays, most engines have a separate ignition coil for each spark plug, called a “coil on plug” setup.
These newer systems with multiple coils are more reliable than the old distributors, but individual coils can still stop working over time. When this happens, it can cause one of the engine’s cylinders to misfire. That means the fuel in that cylinder either doesn’t burn when it should or doesn’t burn at all. This is sometimes called a “dead cylinder.” If misfiring goes on for too long, it can lead to bigger problems like bent piston rods or damage inside the cylinder. It can also let unburned fuel get into the exhaust system, which is bad for the environment and can damage the car’s catalytic converters. So, if you notice a misfire, it’s important to get it fixed right away.
Ignition coils usually last a long time—over 100,000 miles. But eventually, they can go bad and cause a misfire in your engine. At first, you might not notice it much, but it’ll get worse over time. When your engine misfires, even for a short time, the computer that manages your engine will probably notice and turn on the check engine light.
Other signs that your ignition coil might be bad include your car using more gas than usual, it feeling slow when you speed up, and your engine making loud bangs as unburned fuel comes out of the exhaust pipe.
If your engine misfires, it might not just be the ignition coil causing the problem. It could also be a nearby spark plug, bad spark plug wires, or some other electrical problem. When you take your car to a professional, they’ll use special equipment to test the voltage in different parts of the engine to find out what’s wrong. They might also check things like clogged fuel injectors.