How to replace your spark plugs | Autoblog Wrenched

Worn out plugs can hurt your car

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Spark plugs are the heart of your car's ignition system. If yours are worn out, new ones can dramatically improve your performance. See how to replace them here. Watch all of our Autoblog Wrenched videos for more tips on how to diagnose, fix, and modify cars from professional detailer Larry Kosilla. While you're at it, check out Larry's other car cleaning and maintenance video series Autoblog Details!

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The sparky heart of your ignition system

If your spark plugs are worn out, new ones can dramatically improve your performance. Doing it yourself is easier than you think. Make sure the prop rod is securely in place or the hood struts are in good working order, so the hood doesn't fall on you during this repair. It seems like spark plugs last a lot longer these days, but what are the signs indicating they need to be changed? If your car has a rough idle, a decrease in performance, or if you're consuming more fuel, your spark plugs could be a likely culprit. Prior to starting the job, look at your owners manual to find the correct spec plugs for your car and engine.

Know your plugs

There are a few different types of plugs. The basic is copper, while platinum and iridium will last longer. Unless your car is heavily modified, sticking with original equipment spec is usually the best bet. Visit your local auto parts store to buy the plugs, but if they don't have the OEM brand, they can usually cross reference a suitable replacement.

Prep is key

Lay a towel over the fender before you get started to protect the paint as you will be leaning over the engine for some time. On this particular car, we needed to remove four allen bolts to reach the plugs. Remember to mark the location of each wire before you remove anything. Likewise, you can take a quick picture with your phone for safety.

On modern cars, coil packs are used in place of distributors and ignition wires because they provide more efficiency and reliability by using no mechanical or moving parts like distributors. The coil pack is a collection of ignition coils controlled by your car's electronic ignition that transforms the power from your cars battery down to the spark plug, which of course ignites the fuel and drives the pistons. Putting a wrong wire or in this case, a wrong coil pack on a plug, is going to make the engine run terrible or even not at all, so keep track of which plug goes on which cylinder. Remove the bolt holding the ignition coil. Next, unplug the ignition wires connected to the coil. Now, remove the coil by lifting straight up and out of the manifold.

Remove the plug

With all four coils unplugged and out of the engine, attach a piece of tape between your ratchet extension and the spark plug socket. This is done to prevent the socket from falling off and getting trapped in the narrow coil pack tube, which would be annoying to retrieve. Gently loosen each spark plug and carefully pull it out of the engine and inspect its color. Notice if each spark plug looks the same or drastically different and which cylinder they came from. It might be helpful for trouble shooting future engine issues down the road.

Mind the gap

Most new plugs come pre-gapped for your car's engine. If not, use a gap tool to carefully adjust the air gap or the space between the electrodes. Slide the plug on the standardized tool and adjust the distance to meet your manufactures' suggested gap. Next, add a bit of anti-seize on the threads, but be careful and avoid getting them on the electrodes. Some plugs come pre-coated and do not require additional anti-seize, but check the box description.

Carefully reinstall the plugs

To reinstall the plugs, here's a very simple trick to avoid cross threading the plugs, which would require a full engine tear down to correct. Any random hose that fits over the top part or terminal snuggly will work. This will allow me to hand screw the spark plugs without cross-threading because the rubber hose will bend or flex if the threads become stuck, unlike a metal extension, which will power through and crush the soft threads. Pretty nifty idea. Once the threads are started, then use a ratchet extension and give the plug about a quarter turn under tension but no more as you could break the porcelain if you over tighten.

A little dab'll do ya

Before replacing the coil, add a dab of dielectric grease to the tip prior to installing it over the spark plug terminal. Plug it back in to the ignition wires. You will hear and feel a click when it's seated properly on the plug. Screw down the coil to the manifold, repeat this step for all cylinders, then, replace the manifold cover when you're done.

Start the engine to test the idle

If it doesn't start immediately, check to make sure all the coils are plugged in and the wires are fully seated. The ignition system on our cars can be intimidating. But by taking your time and doing the proper preparation, you could bring your car's performance back to factory specs and save a bunch of money too. For more how-to car repair videos, visit

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