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How to Replace Your Spark Plugs

How to Replace Your Spark Plugs

Last Updated September 20, 2024 | Bill Tumas

Your spark plugs are an essential component of your car's engine. Your car won't even start without functioning spark plugs, so it's important to make sure your spark plugs are in tip-top shape. If you're interested in learning more about spark plugs, read our article on what spark plugs are and the differences between different types of plugs.

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How to Change Your Spark Plugs

In this article, we're going to answer the question of how do you change a spark plug. We performed this installation on a 2013-2017 Ford Focus ST, but the process is largely the same for most gasoline-powered production vehicles on the market today.

This is a simple install and can be done by beginner mechanics with simple tools. For a more in-depth guide on how to replace your spark plugs, check out the video below.

The following list of tools is needed to replace the spark plugs on a Focus ST, but the tools you'll need for your car will differ slightly. Keep that in mind and find what's necessary for your car. You'll be working with electronics, so it's a good idea to disconnect your battery before you start working. Here are the tools needed to replace spark plugs.

Tools Needed:

  • 3/8 Ratchet
  • 5/8 Spark Plug Socket OR 5/8 Deep Socket
  • 6" Extension
  • 1/4" Ratchet
  • 8mm Socket
  • Spark Plug Gapping Tool
  • Torque Wrench
  • Anti-Seize

Step 1: Remove the Engine Cover

Carefully remove the engine cover to access the top of the engine and spark plugs.

Mechanic removing the engine cover on a Ford Focus ST

Step 2: Loosen the Metal Clamp (Optional)

If you're running an aftermarket cold air intake, there's a good chance it'll be in the way of your coil packs. If this is the case, you're going to need to remove it. Skip this step if you don't have an aftermarket intake.

Start by loosening the clamp connecting the intake to the rubber hose above the coil.

Mechanic loosening a metal clamp on an intake

Step 3: Remove Mounting Screws (Optional)

Then, remove the two mounting screws holding the aftermarket intake in place.

Mechanic removing the mounting screws holding the intake in place

Step 4: Remove the Intake from the Rubber Hose (Optional)

Then, slide the intake out of the rubber hose and push it back toward the firewall. This gives us enough room to access the coil and change the spark plugs.

Mechanic removing the rubber hose from the intake

Step 5: Move the Wiring Harness

Move the wiring harness to access the coil hardware by pulling up on it. Then, move it out of the way.

Mechanic moving the wiring harness from the coil

Step 6: Disconnect the Plug

Then, disconnect the plug on the front of the coil.

Mechanic disconnecting the plug on the coil

Step 7: Remove the Coil

Loosen and remove the bolt holding the coil in place. Then, pull the coil out from your engine.

Mechanic unscrewing the bolt holding the coil in place

Step 8: Remove the Spark Plug

After you've removed the coil from the engine, use your 5/8" socket to remove the spark plug from the engine.

Mechanic holding a 5/8 inch socket

Step 9: Gap your Spark Plug

Your new spark plugs will come with a gap of somewhere between 40 and 50 thousandths. You're going to need to gap them according to your car's manufacturer's specifications. For the Focus ST, we recommend between 30 to 32 thousandths.

Mechanic gapping their new spark plug

Step 10: Apply Anti-Seize

Before installing the new spark plug, apply some anti-seize to the threads of the spark plug to prevent them from getting stuck in the head of the engine.

Mechanic applying anti-seize to the threads of a new spark plug

Step 11: Install the New Spark Plug

Then, using your 5/8" socket, install the new spark plug by tightening them into place on the engine.

Mechanic screwing the new spark plug in

When tightening your new spark plugs, be sure to use a torque wrench and torque them to the spec recommended by the plug manufacturer.

Step 12: Reinstall the Coil

Slide your coil back into the engine and reinstall the bolt holding it in place.

Mechanic screwing in the mounting screw for the coil

Step 13: Plug in the Engine Harness

Plug the engine harness back into the connector located on the coil.

A plugged in wiring harness on the coil

Step 14: Repeat the Process

Repeat steps 5-13 on each of the other cylinders.

Step 15: Reinstall the Intake (Optional)

After you've installed the new spark plugs, reinstall your intake if you had to move it at the beginning of the process.

Mechanic reconnecting the intake to the rubber hose

Reconnect the intake to the rubber hose, then tighten the hose clamp. Then, tighten down your mounting hardware.

Step 16: Reinstall the Engine Cover

Reinstall the engine cover by snapping it back into place.

Mechanic reinstalling the engine cover on the Focus ST

Congratulations, you're all done!

Save the Money and Do It Yourself

Changing your spark plugs is a simple process that is perfect for beginner mechanics looking to do some important maintenance on their ride. Getting your spark plugs changed at a shop can cost a few hundred dollars, so next time you need new spark plugs, save the money and do it yourself.

Check out our selection of Mustang spark plugs if you need some for your ride.


About the Author
Bill, our resident Mustang expert, brought over 25 years of experience in the auto industry. He produced hundreds of videos as the host of the CJ Pony Parts YouTube channel.
This article was researched, written, edited, and reviewed following the steps outlined in our editorial process. Learn more about our editorial standards and guidelines.