While most newer vehicles use a coil-on-plug (COP) design for ignition, older vehicles still need plug wires to get the spark from the distributor to the plugs. The spark plugs themselves can serve anywhere from 30K to 100K miles before needing replacement, but the wires can degrade and crack much sooner.
Changing plugs and plug wires is an easy job (just remember to replace one plug wire at a time to preserve proper firing order). Shop Advance for spark plugs and plug wires from top brands like Carquest, ACDelco, DENSO, Ford Motorcraft, Champion, NGK and Autolite.
The distributor was replaced by a distributor-less ignition system (DIS) that uses a computer, camshaft position sensor and crankshaft position sensor to determine spark timing. The DIS system uses one or several coil packs to generate spark. On vehicles with waste-spark DIS, one ignition coil pack will fire two spark plugs.
Today the most common DIS ignition system is the coil-on-plug (COP) ignition system. Each cylinder has a dedicated ignition coil for each spark plug; most often with the ignition coil sitting directly above the spark plug. Plug wires have a finite service life and tend to 'leak' current when they get greasy, dried-out or generally worn.
Here's a quick way to see if your spark plug wires are getting to the end of their lifespan: drive to a very dark spot at night, pop the hood with the engine running, and use a spray bottle to lightly spray a mist of water up and down the plug wires. If they're starting to fail, you'll be able to see arcing between wires.
When replacing plug wires, just be sure to replace only one plug wire at a time and match that wire's length precisely against the old wire. That way you can be sure you're maintaining the original firing order of the engine.
What do spark plug wires do?
Spark plug wires, also known as spark plug cables, ignition cables, high tension leads or high tension cables perform a couple important functions. Their primary purpose is to deliver electrical current to each of the spark plugs from a distributor, ignition coil or magneto. In the process of doing this, they must also suppress electromagnetic interference, which can disrupt on-board computers, wireless signals, radios and speakers.
How long do spark plug wires last?
A quality set of spark plug cables will typically last 60,000 to 70,000 miles. Longevity may vary with brand and use. We recommend replacing your spark plug wires whenever you replace your spark plugs.
What causes spark plug cables to wear out?
Spark plug wires are covered by an insulating heat-resistant material such as silicone or synthetic EPDM rubber, which gradually wears down over time due to the heat passing through the wires. Cables can also be damaged by tugging on them, oil leaks, moisture or terminal corrosion.
When your spark plug wires are starting to wear down, you will usually notice some telltale signs:
There are three main types of spark plug wires:
Replacing spark plug wires involves disconnecting your battery for safety, disconnecting both ends of each old wire and replacing each wire with a new one. To make sure you replace them correctly, take note of how each wire is installed before disconnecting them, or even take a photograph and remove only one wire at a time. Using a special tool called a spark plug boot removal tool will make it easier to replace your wires without damaging your spark plugs. On older vehicles, you may also need to replace your distributor cap. For more detailed instructions, see the article on How to Replace Spark Plug Wires.
How often should I replace my spark plug wires?
To keep your car running in the best shape, you should replace your spark plug wires whenever you replace your spark plugs. For some vehicles, this will be about every 20,000 to 40,000 miles. Consult your owner's manual for the replacement interval on your vehicle.
Can I replace my spark plug wires myself?
Yes, learning to replace spark plug wires is fairly easy. It should take you about an hour once you learn how to do it.
Is there a way to make my spark plug cables last longer or run better?
One way to extend and improve the performance of your spark plug wires is to periodically clean them. You can do this with a rag, WD-40 and dielectric grease. This will also give you an opportunity to inspect your wires for wear and tear.
Buy spark plug wires online or visit your local Advance Auto Parts store and have one of our knowledgeable Team Members help you.