A spark plug is an integral part of your vehicle's ignition system. It is critical to the combustion process inside your engine.
An internal combustion engine houses hundreds of components that work in concert to produce the power needed for your vehicle to move. Anywhere from four to eight pistons move up and down constantly in their respective cylinders, pedaling the crankshaft like you might pedal a bicycle.
A lot of energy is required to keep these pistons moving. So, every other time a piston rises in its cylinder, it compresses a precise mixture of air and fuel. At just the right time, a spark plug ignites the compressed air/fuel mixture, resulting in the rapid release of energy. The expanding gases that are produced move the piston downward toward the crankshaft.
The spark plug itself delivers a tiny yet high-voltage electrical arc in response to the ignition coil. Each cylinder needs a spark plug for ignition. Some engines use two spark plugs per cylinder. Spark plugs are typically replaced as a complete set.
Spark plug replacement is not a particularly complicated service, but it can be quite difficult on some engines. That is because access to the spark plugs is often limited and requires special tools. And if a spark plug breaks before it comes loose from the cylinder, the repair can be significant.
The specific process for replacing spark plugs also differs depending on the age of your vehicle and the type of ignition coil(s) used. Older models featured a distributor that controlled the way each spark plug was fired, the timing between cylinders. On those engines, spark plug wires extended from the distributor cap to each spark plug. Some newer models with electronic ignition rely instead on a set of coils that get their direction from the engine control module. Spark plug wires, in those cases, run from the coils to the spark plugs. The latest technology includes coils that are installed directly on top of each cylinder and spark plug in an arrangement known as “coil-on-plug” or COP.
To remove and replace the spark plugs, a technician must do the following: