Spark plug wires are pretty durable. They aren't a moving part so they don't wear out too often.

But when they do, a damaged spark plug wire can make your car run rough and affect gas mileage. Cracked wires can cause misfires resulting in poor performance. A bad plug wire can even trigger your Check Engine light.

• Network: Auto Service guide

• Community: From the Garage

A careful inspection of your plug wires can avoid any problems.

So do a quick inspection and save yourself a headache. Here's how:

-- Open the hood and locate the spark plug wires. They can be black, blue, red or orange. Most are black. The number of spark plug wires most often corresponds to the number of cylinders your engine has.

-- Don't take all the spark plug wires off at once, even if they're numbered. Remove the spark plug wires one at a time. They must go back on the distributor cap in exactly the same order they came off, or you'll have changed the "firing order" and your car may run badly or not at all. You can cause expensive damage by switching the order of the plug wires.

-- With your engine off, start at the distributor end of the plug wire and work your way toward the plug end. You're looking for anything that is not smooth, pliable rubber.

-- Bend the wires slightly to be sure no cracks appear.

-- Check the boots at the distributor end of the wires to be sure they are not torn or cracked.

-- Finally, check the wires at the spark plug end one at a time by pulling it off the plug and inspecting the end for any tears or cracks. Also look to be sure there is no burning or darkening of the end.

If you find any damage at all, it's time to buy a new set.

Spark plug wires should be changed when they start to become hard or inflexible, or look dry and cracked. If one wire fails, it's probably time to change them all. Spark plug wire life varies greatly depending on a number of factors, but you should change them at least as often as manufacturer's recommendations.

It's also important to keep them clean. A thin film of dirt can form on the outside of the plug wire and around the boots at the ends of the wires can form conductive path to the high voltage when exposed to moisture. The conductive path can drain away the current that should go to the spark plug. If your car misses out or runs rough only in damp weather, you may have this type of wire problem.

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