How to Change Spark Plug Wires

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When Do You Need New Spark Plug Wires?

Spark plug wires need to be replaced.
Installing new spark plug wires is good preventive maintenance. photo by Matt Wright

Spark plug wires are one of the more neglected parts of most engines. It's not that they don't go bad, but most people don't replace their plug wires until one of them is so bad it's causing their engine to run badly. Did you know that one of the major causes of Check Engine Lights is a bad plug wire? A faulty spark plug wire can cause an engine misfire, which will trigger the light and cost you a trip to the repair shop to turn it off. I recommend new spark plug wires every 30,000 miles or so. They can last much longer, but when they go bad, you'll spend much more time and money on the repair than you would have on the prevention.

The point is this: Spark plug wires are easy insurance against a breakdown. Take the time to replace them, and you'll be doing yourself a favor. Do the job while you install new spark plugs, and you're saving time.

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Getting the Lay of the Land

Your engine cover may reveal plug wires ... or trouble.
Remove your engine's decorative engine cover to see if your spark plug wires are easily accessible, or if you're looking at a long afternoon of work. photo by Adam Wright, 2010

This may seem like a superfluous step in the process, but it's major. If you're working on a 4-cylinder engine, a straight 6, and most V8 engines, your job is probably very easy. Now's the time to take a look at your engine to see if you can easily reach all of the spark plug wires. Remove the "fashion cover" that hides all of the engine components, and see if you can see all of the plug wires and access holes. If you can, you can skip to this simple step and celebrate. Your job is easy.

If you can't easily reach all of your plug wires, your afternoon just got longer. In many modern engines, half of the spark plugs are way out of reach, and replacement requires removal of one or more engine components. The following how-to steps will guide you through a typical replacement that involves difficulties such as this. Take it slow, and take notes -- you shouldn't have any problems!

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Disconnect the Air Box

Removing the air box to facilitate spark plug wire installation.
Remove the airbox to free the intake plenum for removal. Spark plug wires hide beneath!. photo by Adam Wright, 2010

If you've made it this far, you have an engine that makes it very difficult to change your plugs and wires. Don't sweat it. Your day may be longer, but take it step by step, and you won't have any problems.

The first step is to remove the air box. The air box contains your air filter, and connects to the large intake plenum that you can see is hiding the rest of your spark plug wires. If you have a large flexible hose connecting the airbox to the plenum, you can remove the clamps that hold the hose on each end, and remove the hose, leaving the air box in place. If your air box and hose are one unit, you'll have to unbolt the entire box.

Before removing the hose or the box, check to see what electrical connections you may need to disconnect first.* *If you want to be sure you properly reconnect your electrical plugs, take a digital photo of the air box setup before you remove anything, or draw a diagram to aid your memory.

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Remove the Intake Plenum

The intake manifold is your barrier to accessing the spark plug wires.
Removing the intake plenum to access the spark plug wires. photo by Adam Wright, 2010

Before you can remove the intake plenum, there are a number of electrical connections, cables, nuts, bolts and who knows what else for you to deal with. Take your time. Start with all of the electrical plugs.

A digital photo may help you remember where all of these connections are. You'll also need to disconnect the accelerator cable from the throttle body on the back of the intake plenum (if your car is equipped with a cable). Now you need to remove all of the nuts and bolts holding the intake onto the head, and there will be lots. Brackets, studs, and threaded holes all hold this thing on.

Take your time and visually move over every inch of the intake before you start to pull and tug. It may take a little force to remove, but be sure you've reached that point before you start to go for it. Sometimes the gaskets can act a little like glue, holding things together tightly. If you think this is the case, a few taps with a soft mallet can help get things moving.

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Remove and Replace the Spark Plug Wires ... Finally!

Ready to install those plug wires.
Install your spark plug wires one at a time. photo by Adam Wright, 2010

With all of the junk removed, you can finally see those spark plug wires sticking out of the back of the engine! WAIT! Don't start yanking them out just yet. You need to replace the plug wires one at a time to ensure you don't mix up any of the connections. Replacing them one at a time ensures they will be reinstalled in the correct location. Also, I find that it helps to lay all of the new spark plug wires out on a clean table so that you can best match up the old wire with the new one according to length.

And hey, while you have the wires off, it's a great time to replace the spark plugs! You didn't do all of that work just to have to do it again the next time you need a tune up.