How to Change Spark Plugs

It's gotten a little more complicated to learn how to change spark plugs. Older vehicles still use spark plug wires. Newer cars feature the wasted spark system, which uses one coil for every two spark plugs. The most recent system is the coil on plug system, which has a coil on every spark plug. This system does not use spark plug wires, but a spark plug boot attached to the coil.

Spark plugs come in a 5/8-inch version and a less popular 13/16-inch version. Most all have 12mm threads. A 3/8-inch drive ratchet, a 6-inch extension and the appropriate socket are needed to remove the spark plugs. Other tools may be needed to access the spark plugs depending on the year and model of your car.

Standard Spark Plug Wire Engines

If the vehicle has a standard ignition system using one distributor and spark plug wires, start by removing one wire at a time by twisting it slightly to loosen and pulling the wire off. Use the appropriate socket and remove the spark plug. Gap the spark plug before installation using the placard under the hood stating the spark plug gap. Place a small amount of anti-seize compound on the threads to facilitate removal at a later date. Install some silicone spark plug boot grease in the boot to also facilitate removal. By replacing one spark plug at a time, there will be no problems with the firing order.

Vehicles With A Wasted Spark System

These vehicles use coils with two spark plug wires to each coil. Replacement of the spark plug remains the same. One at a time is the most trouble free method.

Coil On Plug Ignition Systems

These systems found on most of the late model vehicles use one coil for every spark plug. The coil sits directly on top of the spark plug or in the immediate proximity. If the coil is on the top of the valve cover it must be removed to access the spark plug. Usually it takes a 10mm socket or wrench to remove the two bolts securing the coil to the valve cover. Always disconnect the electrical connector prior to removing the coil to eliminate any possible damage to the wires, connector or pins. The coils are expensive, so don't take any chances. Remove the two bolts and lift the coil off the plug. From this point, it is good to have a magnet or a piece of vacuum hose to remove the plugs once they are loose. They sit pretty deep in the cover and are difficult to reach.

Always replace the spark plugs with the factory recommended style plug. Platinum plugs and different variations considered longer lasting are fine as long as they meet the vehicles standards. Avoid spark plugs with variations in the ground strap or electrode unless the vehicle is modified or research has been done on this type of spark plug for this particular application. There is a good reason for this. Some vehicles won't even start or will barely run with the same type of plug but a different brand. Remember the adage, you get what you paid for. Different spark plugs may look the same but have different resistance and need more power to fire. If the vehicle is designed for fuel economy, you can bet the manufacturer did not install a killer ignition system. The average vehicle delivers 18,000 to 20,000 volts. Throw a set of plugs in that requires a higher voltage to jump the gap and the spark goes away or is diminished to the point performance will suffer. Stay within the recommended heat range unless modified so detonation or poor performance is not incurred.

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