Ignition Coils are found on almost all gasoline powered internal combustion engines. They supply high voltages to spark plugs for proper fuel combustion inside engine cylinders. These car ignition coils are a crucial component to your car's overall performance and fuel efficiency. As with other parts of your car, these ignition coils will degrade over time and will need to be replaced at some point. A bad ignition coil can cause problems with your vehicle's fuel economy, as well as a number of other unpleasant symptoms like backfiring and unburned fuel escaping the exhaust system.

Ignition coils are basically a coil of wire wrapped around a core, and they produce the high voltage spark needed to ignite the air/fuel mixture. The physics of it all is pretty simple: changing current in a wire induces a changing magnetic field and vice versa, and that changing magnetic field then induces a voltage in the secondary part of the coil. That high voltage spark travels through several components including a distributor and the spark plug wires to get to your engine's spark plug, where it creates a spark that burns the air/fuel mixture and starts your car's engine.

In older cars with traditional distributor ignition, the ignition coil looks like a small metal cylinder (sometimes called a canister-type coil) with wires sprouting from it. One of those wires connects it to battery voltage, another to the contact points in the distributor, and the central high-tension lead goes to the center of the distributor cap. With this setup, the ignition coil's primary winding contains a number of coarse turns of wire and the secondary winding has very fine wires with many more turns. When the electrical circuit is closed between the battery and the primary winding of the ignition coil, the bouncing spring (the condenser in the center of the coil) causes a current to flow through that secondary winding for a short time, creating and then collapsing a magnetic field. That magnetic field induces a voltage in the secondary winding, and that induced voltage is then used to fire the spark plug at the exact moment it's required.

Modern vehicles with multiple-coil pack or coil-on-plug systems use ignition coils that are packaged in modules. While these are much more reliable than the single coils of older distributors, they still fail over time. Typically, you'll start seeing engine misfires in a particular cylinder as the ignition coils degrade. These problems are a real pain for your engine and a waste of the fuel you're paying for.