What is an ignition coil?

An ignition coil is a quadripole that uses electromagnetic induction to generate a pulse that creates a very high voltage at the secondary end of a step-up transformer1. An ignition coil is a mechanical part found only in gasoline-powered vehicles. Its purpose is to deliver high-voltage current to the spark plugs, enabling them to produce the spark needed to ignite the air-fuel mixture. The ignition coil is a central element in an engine because it controls the operation of the spark plugs. Without an ignition coil, or in the event of a failure, the engine will run poorly.

What does the ignition coil do?

The ignition coil is made up of two parts: a primary winding that is supplied with 12 volts, and a secondary winding that is connected to the spark plug and ranges from 10,000 to 30,000 volts. Ignition coils are like compact electrical transformers.  It's the ignition coil that creates the spark needed for combustion.

To do this, the coil stores the current sent from the battery and then sends it to the spark plugs to create a spark in the cylinders. The coil also synchronizes the spark plug firing.

In older cars, the engine had a single ignition coil.

Today's cars have multiple coils that control multiple spark plugs. In modern cars, each coil is connected to a spark plug, which is responsible for creating the spark that ignites the mixture. Each spark plug requires approximately 15,000 to 20,000 volts of electricity to do this. Therefore, the coil must provide a high enough voltage for the spark plug to create the arc that produces the spark.

What are the different types of spark coils?

The classic ignition coil

This is the type of coil found on older models. A single coil supplies high-voltage current to all spark plugs through an ignition head.

The high-voltage distributor coil

The high-voltage distributor coil does not use the distributor head to deliver power. It consists of two coils, each supplying power to two spark plugs simultaneously. This coil handles the power transfer without the need for ignition heads.  Wires are used to transfer current between the components.

High voltage distributor ramp coil

Do not use the distributor to deliver power.  The ramp coil has two coils, each feeding two spark plugs at a time. This part consists of a block that fits directly onto the spark plugs, with no connecting wires. It can be converted to a single block. This coil manages current transfer without the need for ignition heads.

Double independent coil

This coil does not use the ignition head for power. It consists of two coils, each of which powers two spark plugs at a time. This coil handles the power transfer without the need for ignition heads. It is placed directly on the spark plugs. Each coil can be replaced independently.

The pencil coil

Named for its shape. This is the most common coil, and each one is connected directly to a spark plug. These are independent coils.

Symptoms of a bad coil

An engine that has difficulty starting.

Modern engines have multiple ignition coils, and if one of them fails, you may experience ignition problems and difficulty starting the engine. Be careful, however, as this symptom is not always automatically associated with a coil problem.

Misfiring in one or more cylinders.

Misfiring means that one of the engine's cylinders is not firing properly. In a lost-spark ignition system, the coil supplies power to two spark plugs, so if it's defective, two cylinders may misfire.

Increased fuel consumption.

When your spark plugs aren't getting enough power (because of a bad coil), the system tries to compensate by injecting more fuel. A faulty air mass sensor or a clogged engine filter can also cause excessive fuel consumption.

The engine trouble light on the dashboard.

This light can indicate some problems, including ignition coil issues. In this case, an OBD-II check can be performed to determine a diagnosis. Use a diagnostic kit or go directly to your service center. Codes P0300 through P0312 indicate misfiring, while codes P0350 through P0362 indicate coil problems.

Oil leak.

The tremendous amount of current and charge transformed inside ignition coils causes them to dissipate a lot of heat. When the part is operating normally, oil usually helps to dissipate this thermal energy. However, if the coil is damaged, it can overheat and eventually crack the housing. The oil then begins to leak.

Bad spark plugs.

When spark plugs are faulty or worn, they can often draw more power than the engine is designed to handle. This puts too much stress on the ignition coil, which eventually becomes damaged. If you notice problems with the spark plugs, it's a good idea to check the ignition coils as well.