Why Spark Plug Wires Are Important

Spark plug wires are the short cables that connect your car’s spark plugs to the distributor. Some vehicles have “on plug” coils, in which case the wires connect to this device rather than the distributor, but still function in the same way. Although you may not hear a lot of talk about spark plug wires, they are very important in maintaining both the performance and functionality of your vehicle, and should be changed periodically. The process is not difficult and can be done at home in about an hour.

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Spark Plug

Basics Of Spark Plug Wires

Originally, spark plug wires used actual metal wires, but that is not the case anymore, even though the name hasn’t changed. Whether your drive a Nissan or Toyota, today’s spark plugs use carbon filaments surrounded by insulating shields. Each time a current is passed through the wire, the carbon breaks down a tiny amount, causing the wires to slowly degrade. This can cause arcing, or short-circuiting of the wire with the engine or other metal components. Another possibility is increased resistance in the wires. Both situations will cause decreased engine performance, reduced fuel mileage, and eventually lead to skipping or rough operation of the engine.

When To Change Plug Wires

Your vehicle owner’s manual will stipulate when the manufacturer recommends changing the spark plugs. As a rule, spark plug wires should be changed each time the plugs themselves are changed. The replacement period will vary somewhat from one vehicle to another but equates to changing the plugs and wires at least every 60 to 100 thousand miles. Popular Mechanics offers a couple of tips for determining wear on your spark plug wires, such as dampening the wires and checking for arcs using a well insulated screwdriver.

Selecting The Best Replacement Wires

The parts of your engine are like a jigsaw puzzle, with every part fitting together in a specific way. Using plug wires that do not meet Original Equipment Manufacturer specifications can result in more frequent replacement, poor engine operation, or even spark plug wires that do not fit well or connect properly. To get the best performance from your car, always buy OEM spark plug wires. They will not cost much more and will typically result in an overall savings in fuel economy and engine performance.

The Right Tools For The Job

There are only two specialized tools used in changing your spark plugs and wires. The first is called a spark plug boot puller, or boot pliers, and is used to remove the rubber insulator that slides down over the top of the spark plugs. The second is a spark plug wrench or socket, used to remove the plugs themselves. Spark plugs come in different sizes, but each vehicle only uses one. Both of these tools are inexpensive and will last indefinitely with proper care. On some vehicles, you will also need a pair of needle-nosed pliers to remove small clips connecting the wire to the inner side of the distributor cap. Finally, if the set of wires you purchase are not pre-treated with dielectric grease, be sure to purchase it separately.

Document The Firing Order

The first– and one of the most important– step in spark plug wire replacement is to document the firing order. Firing order is the pattern the wires take in connecting to the distributor, and your car will not operate correctly if the order is wrong. Family Handyman recommends taking a digital image of the wiring before you begin, but you can also draw a simple diagram if a camera is not available. The importance of this step cannot be overstated, and failure to document correctly will almost always result in a car that will not function.

One Step At A Time

Replace one wire at a time, rather than pulling them as a group. This will ensure the proper firing order and that each wire follows the path intended for it. Even a mistake as simple as swapping wires in a wiring harness or retaining clip can cause arcing or electrical interference. Before connecting each end of a wire, apply dielectric grease. This prevents the boot from sticking and promotes a solid electrical connection.

Changing your spark plugs and wires is only one of several procedures involved in a vehicle tune-up. On most newer vehicles, a complete tune-up will also include resetting the vehicle computer, which can only be done by an authorized mechanic using special equipment. Doing some of the minor tasks like changing the plug wires and the air filter will reduce your total labor costs, but will not completely eliminate the need for a certified mechanic.