DIY

How to Change Spark Plugs

Reading Time: 5 minutes

Spark plug replacement is one of the most common maintenance procedures. The job seems easy in theory, which is why many vehicle owners want to attempt it themselves.

And it’s true⁠—on some vehicles, spark plug replacement is relatively easy. On others, however, the job can be difficult because the plugs are tough to reach.

So, if you’re a newbie, before you decide to tackle replacing your spark plugs, you first need to find out whether they’re easy to access.

On four-cylinder engines, the plugs are often located underneath the ignition coils that sit right on top of the engine. If your vehicle has this design⁠—and you’re feeling brave⁠—you might consider replacing the plugs yourself.

old and new spark plugs

Spark Plug Replacement: How-to

Spark plugs do what their name implies—they ignite or “spark” the air/fuel mixture inside the engine. The result is a series of controlled explosions that set the engine’s pistons in motion. Each piston helps to turn the crankshaft, thereby creating the rotational force needed to propel your car down the road.

Usually, there is one spark plug for each of the engine’s cylinders. The plugs are considered a maintenance item that should be replaced at the interval suggested by the vehicle manufacturer.

You’ll find that information listed in your owner’s manual.

Now⁠—are you ready to replace your car’s spark plugs? Good, then let’s get started!

Tools Needed to Replace Spark Plugs:

The tools needed to replace spark plugs will vary, depending on what type of car you have.

In general, however, you’ll need:

Spark Plug Replacement Instructions (Typical 4-Cylinder Engine):

Before we begin, keep in mind: all vehicles are different. The information below is generic and for entertainment and educational purposes only. Be sure to follow the repair information for your specific application.

Repair manuals, such as those from Chilton, are useful, but a subscription to a repair database is even better. ALLDATA and Mitchell 1 both have single-vehicle subscriptions for DIYers that provide detailed factory repair information.

You can learn more about accessing quality repair information in this article.

spark plugs location
The spark plugs are located underneath the ignition coils on this 2007 Honda Civic.

Spark Plug Removal on a Typical 4-Cylinder Engine:

  1. Put on your safety glasses.

  2. Make sure the engine and ignition are both off. The engine should also be cool.

  3. Use compressed air to remove any dirt or debris from around the ignition coil. Use a rag if an air compressor is unavailable.

  4. Remove the ignition coil electrical connector. Usually, this involves pushing down on the connector’s tab while pulling the connector away from the coil. 

  5. Use a ratchet and socket to remove the ignition coil retaining fastener(s).

  6. Pull the ignition coil up and away from the engine to remove it from the spark plug.

  7. Use a ratchet, extension and spark plug socket (with a rubber insert) to reach the spark plug inside its bore.

  8. Turn the spark plug counterclockwise to loosen and remove it from its bore.

  9. Repeat the above steps for each spark plug.
removing ignition coil connector
Removing the ignition coil electrical connector.
removing ignition coil fasteners
Removing the ignition coil retaining fasteners.
removing ignition coil
Removing the ignition coil.
spark plug inside the bore
Using a ratchet, extension and spark plug socket (with a rubber insert) to reach the spark plug inside its bore.
removing spark plug
The spark plug removed from its bore.

Spark Plug Installation on a Typical 4-Cylinder Engine:

  1. Compare the new spark plugs to the old ones to ensure that both are the same design.

  2. Even if you’re installing a pre-gapped spark plug, you should check the air gap to ensure it was set correctly at the factory.

    Here’s how you can check the gap with a coin-style tool:
    -Consult a repair manual or repair database to determine the correct gap for your plugs.
    -Insert the spark plug gapping tool between the spark plug’s electrodes.
    -Run the edge of the tool in between the electrodes to determine the measurement.

    Note: You can also use a wire-style gapping tool (instead of a coin-style tool) that has built-in adjustment prongs.

  3. Some copper spark plugs do not come pre-gapped, so the gap must be set by hand. To do this, measure the gap as outlined in step #2. Then, use a spark plug gap adjustment tool to increase or decrease the gap as needed.

    Warning: You should never attempt to adjust the gap on platinum or iridium spark plugs as the electrodes may get damaged.

  4. Coat the spark plug threads with a light application of anti-seize.

  5. Place the spark plug into the insulated spark plug socket. Then, use the extension to carefully thread the plug into the engine by hand. Be sure not to cross-thread the plug⁠—doing so can easily damage the threads in the cylinder head.

    Note: If the plug does not go in easily, the threads in the cylinder head may need to be cleaned using a thread-chasing tap.

  6. Use a torque wrench to tighten the spark plug to the manufacturer’s specification. This information can be found in either a repair manual or an online repair database.

  7. Position the coil over the spark plug.

  8. Make sure the coil’s mounting hole lines up with the stud or hole on the engine.

  9. Press down on the coil gently.

  10. Reinstall the coil retaining fastener(s), then use a ratchet and socket to tighten it until it’s snug. If you’re unsure how tight the fastener should be, use a torque wrench to tighten it to the manufacturer’s specifications. This information can be found in either a repair manual or an online repair database.

  11. Reinstall the coil electrical connector. You’ll hear it click once it’s securely in place.

  12. Repeat the above steps for the remaining spark plugs.

  13. Start the engine to check your work.
checking spark plug gap
Checking spark plug gap (Note: an old plug is being used for demonstration purposes).
threading spark plug
Threading the spark plug in by hand.
tightening the spark plug
Using a torque wrench to tighten the spark plug to the manufacturer’s specification.
positioning the coil
Positioning the coil over the plug and making sure it lines up with the stud.
tightening the coil
Tightening down the coil retaining fastener.
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Author

Mia Bevacqua

Chief Mechanic at CarParts.com

Mia Bevacqua is an automotive expert with over 15 years of industry experience. She holds ASE Master, L1, L2, and L3 Advanced Level Specialist certification, as well as a bachelor's degree in Advanced Automotive Systems.

Throughout her career, Mia has applied her skills toward automotive failure analysis inspections, consulting, diagnostic software development, and of course, freelance writing. Today, she writes for companies around the world, with many well-known clients showcasing her work.

Mia has a passion for math, science, and technology that motivates her to stay on top of the latest industry trends, such as electric vehicles and autonomous systems. At the same time, she has a weakness for fixer-upper oddballs, such as her 1987 Chevy Cavalier Z-24 and 1998 Chevy Astro Van AWD.

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