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An ignition coil is a key component in a vehicle's ignition system. Generating thousands of volts, the ignition coil sends energy in the form of an electric spark to the spark plugs. This spark is what is used to ignite the air and fuel mixture and start the engine and keep it running. In early automobile designs, a single ignition coil was used to create the spark for all of the engine's spark plugs—modern engine designs use a separate coil on plug ignition coil system. This means that each spark plug in the engine has its own ignition coil mounted on the valve cover which powers only the one spark plug.
Points-type ignition systems used a set of breaker points to determine when the ignition coil would send its electric charge to the spark plugs. Modern ignition timing is controlled by the vehicle's computer system, which is controlled by a computer program. Performance-enhancing chips that reconfigure the computer's programming can be purchased and installed. This alters and creates new timing parameters as well as fuel mixtures and shift points to create a more performance-orientated vehicle.
The ignition coil is basically a container full of tightly coiled copper wire situated in an oil solution. Electricity from the ignition system is sent through the coiled wire, where it is amplified many times over. Some performance ignition coils produce 85,000 volts while the typical family sedan produces 30,000 volts. The higher the voltage output, the hotter the spark at the plug gap. A hotter spark produces more power and better ignites the air and fuel mixture.
The ignition coil should be checked occasionally for cracks and loose wires. Often the best method of testing a coil involves starting the engine and opening the vehicle's hood in the dark. A cracked coil will produce sparks as it fires the spark plug—the sparks can be difficult to see in the sunlight, though they are very obvious when seen in the dark. Any coil seen producing sparks should be replaced immediately. Cracked spark plugs can be located in the same manner.
When replacing spark plug wires or coil wires, it is best to place a small amount of dielectric grease in the wire's boot. This will make removal of the wire much easier as well as protect the wire from moisture. The grease also makes sliding the new wire boots onto the terminals much simpler. All ignition coil wires also should be securely tightened.