An ignition coil boot is an extension of the ignition coil on certain types of modern engine. The boot connects an individual “coil on plug” device to its corresponding spark plug.
All gasoline powered vehicles rely on spark plugs to ignite the compressed air and fuel inside the combustion chambers. The spark plugs receive a high voltage electrical current from a device known as an ignition coil. The coil converts the low current from a vehicle’s electrical system into a more powerful current needed to create the “spark” (actually, it is an electrical arc) that causes the combustion event.
Many vehicles, especially older ones, relied on one or more ignition coils on the engine that were connected to the spark plugs by way of spark plug wires. Newer engines, however, feature “coil on plug” technology, where one ignition coil dedicated to each cylinder is placed directly on the end of the spark plug.
But on some of those engines, the spark plug is located deep inside a narrow depression or well in the engine. The ignition coil boot fastens to the end of the coil and recesses into the spark plug well, where it contacts the end of the spark plug.
An ignition coil boot is a tube typically made of rubber and plastic with a metal spring running through from one end to the other. This spring maintains constant contact with the spark plug and transfers the electricity from the coil to the plug.
One of the signs that an ignition coil boot needs to be replaced is the presence of carbon tracking on one or more of the spark plugs. This occurs when the electricity that is supposed to travel through the spark plug finds an easier path on the outside of the plug. The only way to see the signs of carbon tracking is to remove the ignition coil and spark plug and inspect the components. Plugs with significant carbon buildup can lead to an engine misfire. Therefore, a poorly running engine - or an inspection that reveals a build up of carbon on the spark plugs - are the main signs that the ignition coil boots need to be replaced.
Ignition coil boot replacement mirrors the procedure to replace spark plugs. The complexity of the service varies from one vehicle make and model to the next, depending on how easy it is to access all of the cylinders.
In general, if your vehicle features coil on plug technology, a technician will need to take the following steps to replace the ignition coil boots: