The ignition coil is responsible for producing a high voltage electrical signal powerful enough to create the “spark” needed for ignition. For your internal combustion engine to operate, air and fuel enter the combustion chambers in the form of a vapor. There, the air/fuel mixture is compressed by the pistons, awaiting a source of ignition.
The ignition coils receive low voltage electricity from the battery and convert it to a high voltage before sending it to the spark plugs. When that high voltage current courses through the spark plugs, it jumps a gap between the center and side electrodes. The result is an electrical arc that ignites the air/fuel mixture, creating enough energy to move the pistons to “pedal” the crankshaft and develop power.
On older vehicles, a single ignition coil might send the high voltage current to a distributor where it is “distributed” to each of the spark plugs at just the right moment. Other engines feature electronic ignitions with multiple coils that respond to the direction of a computer module, thereby eliminating the need for a distributor. Or, in the case of many modern engines, a special electronically-controlled coil sits atop each spark plug.
Ignition coil replacement procedures differ from one vehicle to the next. The major differences between these procedures relate to the type of coil(s) used on an engine. For instance, older vehicles that feature a distributor operate with a single coil that is often mounted somewhere in the engine compartment. Distributor-less electronic ignitions might have a bank of coils mounted on top of the engine. And Coil-On-Plug (COP) systems have a coil attached to each spark plug atop the cylinders.
To replace a coil, the battery must first be disconnected. An engine with a bank of ignition coils will require that a technician gain access to the coils by removing any guards, shields, or other components that are in the way. Once the bad coil is identified, it is unplugged from the spark plug wire and disconnected from the wiring harness if applicable. The coil is unbolted, removed, and replaced. The technician must be careful to reinstall the spark plug wires to the correct coils.
With COP systems, a wiring harness plug must be detached from the coil. The coil is then unbolted from the engine and pulled from the top of the spark plug in the cylinder head.