Spark plugs and plug wires. Should they be changed at the same time? Spark plugs take a lot of abuse, and common replacement intervals range from 30,000 miles all the way up to 100,000 miles or more, and even though plug wires aren’t usually listed as replacement items, there are many reasons they should be replaced at the same time as the spark plugs.
Plug wires deliver the high voltage from the ignition coil to the plugs. A plug wire is made up of a conductive material at the core, surrounded by heat resistant, high temperature insulation, as well as specific materials to suppress electromagnetic and radio frequency interference.
As plug wires age, all these materials wear, and can lead to problems such as misfires, poor acceleration, and poor gas mileage. In addition, electromagnetic interference can cause a problem with a vehicle’s computer or sensors, and radio frequency interference is nothing short of annoying.
Another reason to always replace them is carbon tracking. While not necessarily always present, carbon tracking results from high voltage finding an easier path to ground between the plug wire boot along the ceramic plug barrel to the grounded shell.
The carbon will embed itself in the wire boot and ceramic plug barrel, and it won’t go away, even with cleaning. If carbon tracking is present, it’s the equivalent of installing a problem on car.
Even if the wires really aren’t very old, for example replacing plugs with a lower mileage interval, the boots have a tendency to adhere themselves to the spark plugs. They can be difficult to remove, and any twisting or pulling on the wire or boot can affect the integrity of it and lead to failure.
The bottom line is aging, degrading plug wires mean degrading performance and increased potential for failure. Replacing them every time you replace the spark plugs is both a reflection and guarantee of quality.
Whether it’s an older vehicle with leads from the distributor to the spark plugs, distributorless ignition with leads from the coils to the plugs or coil-on-plug systems that only have a boot between the coil and wire, they should all be replaced in the same manner.
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This video is sponsored by Autolite.