How to Change Spark Plugs

Updated on September 4, 2017
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

Changing spark plugs right should not be difficult.
Changing spark plugs right should not be difficult. | Source

With advances in engine management technology within the last few years, it's becoming harder for DIYers to repair and maintain their own vehicles. Now, the Electronic Control Unit (ECU or car computer), and other similar electronic modules, control several systems, even a simple task as changing a flat tire can get you in trouble. You may break a speed or tire-pressure sensor.

But if you learn how to change spark plugs, you'll learn one of the few remaining must-do maintenance jobs the average car owner can still do at home.

So go ahead and replace those old spark plugs in your vehicle. Here, you'll find the tips you need for a successful job.

Changing spark plugs requires some common tools.
Changing spark plugs requires some common tools. | Source

Tools and Materials

Fortunately, you are likely to have most tools you'll need for this job. But, if you need to buy one or more of these items, you'll soon recoup the investment with the improved gas mileage and overall performance you'll get after installing the new spark plugs. So here is the list:

  • Vehicle repair manual: Includes the specifications you need to replace spark plugs and other components, illustrates and breaks down other other maintenance tasks you can do, and comes with a troubleshooting section. Haynes is a good brand of aftermarket manual (make sure you get the edition for your particular car's make and model).
  • Wire feeler gauge: Make sure the one you buy comes with the gauge wire that fits the spark plug gap specified in your vehicle repair manual.
  • Torque wrench: you'll need to tighten the new spark plugs to specification.
  • Spark-plug-wire removal pliers: The pliers help you disconnect plug wires that you can't easily reach by hand.
  • Ratchet
  • Ratchet extension: This tool gives you extra clearance to help you reach and remove spark plugs using your ratchet.
  • Ratchet universal joint: Helps you turn your spark plug socket from different angles.
  • Spark plug socket: This special socket comes with an internal rubber piece to hold the plug inside the socket as you remove it from the engine.
  • Small, soft brush and/or bicycle pump: To remove dirt and debris from spark plug wells.
  • Anti-seize compound: To prevent new spark plugs from bonding tightly to the cylinder head. Using this makes it easier to remove them at the next maintenance interval.

Choosing the right spark plug for your vehicle make and model.
Choosing the right spark plug for your vehicle make and model. | Source

Buying the Right Spark Plugs

After gathering the tools you'll need for this repair job, you need to decide what type of spark plugs to buy.

The best plug for your vehicle is the one recommended by your car manufacturer since engineers built your engine with a specific spark plug in mind. You'll find the suggested spark plugs for your vehicle in your owner's manual, a decal inside the engine compartment, or your repair manual.

Still, you have other options. The most common types of spark plugs are copper, platinum and iridium. Copper conducts electricity efficiently so you can't go wrong with copper plugs if your manufacturer recommends these type of plugs. Platinum plugs can run for 50,000 miles (around five years) or more; and iridium plugs may pass the 100,000 miles (around ten years).

Although some manufacturers of these newer types of spark plugs maintain their plugs offer better performance over copper spark plugs, many drivers say they don't see a performance improvement over copper plugs.

Performance aside, you still have two main reasons to go with platinum or iridium plugs:

  • First, you won't have to worry about replacing the spark plugs again within the next five or ten years, if you like keeping your vehicle in reasonable good shape.
  • Second, on some vehicle models you need to move the engine a few inches to install one or more spark plugs. So a spark plug with a longer service life helps you avoid going through the same time-consuming procedure soon.

How to Change Spark Plugs

Once you have the tools, materials and the correct spark plugs, it's time to get your hands dirty.

  • Before you start though, make sure the engine is cool.
  • And work on one spark plug at a time. That is, remove and install a plug and reconnect the corresponding wire or coil-on-plug assembly. It'll keep you from mixing wires or coils and upsetting engine performance.

Do you think you still need to remove all the spark plugs at once? Number the wires or coils using a piece of masking tape, so that you know how to replace them in their original location.

Removing the Spark Plugs

  • If your ignition system uses spark plug wires--ignition systems with distributors or ignition coil packs--grab the wire's boot to disconnect it from the spark plug. Twist the boot back and forth as you carefully pull it off the spark plug. When an engine component prevents you from reaching the wire's boot, use the spark plug wire removal pliers.
  • If your ignition system uses coil on plugs, consult your repair manual to remove the coils from the plug. In most cases you'll just need to unplug the coil's electrical connector and possibly remove one or more screws. However, on some car models, you need to remove an ignition coil assembly.
  • Once you've reached the spark plug you'll be working on, clean around the spark plug's seat--the plug well--by sweeping off dust and debris using the small soft brush and/or your bicycle pump. This prevents dirt and other foreign matter from falling into the combustion chamber, scratching the cylinder wall and creating an oil leak inside the chamber.
  • When ready, remove the spark plug using the spark plug socket, ratchet extension and ratchet. Sometimes, you need to use a universal joint to unscrew the spark plug at an angle. Install the joint between the socket and ratchet extension.

Installing the New Spark Plugs

Most spark plug manufacturers gap the spark plug at the factory (the gap is the distance between the center and side electrodes, located on one end of the spark plug). Yet, it's a good idea to double check that the gap is correct. With the correct gap, the spark plug provides a healthy spark and prevents cylinder misfires and other engine performance problems.

  • Use the wire feeler gauge to gap the plug. Tap the spark plug electrode on a wooden surface to narrow the gap, or use the feeler gauge tool to slightly pull on the electrode to open the gap. You'll find the correct gap measurement for your spark plugs in your vehicle repair manual. When the plug electrodes have the correct gap, you'll feel the wire gauge slightly dragging as you push it back and forth between the spark plug electrodes.
  • Before installing the new plug, apply a dab of anti-seize compound to the spark plug threads. This makes it easier to remove the plug next time.
  • Install the spark plug finger-tight first. For this, use only the spark plug socket and ratchet extension--and joint, if necessary. This way you avoid cross-threading the spark plug.
  • Using the torque wrench, tighten the spark plug to the specified torque recommended by your car manufacturer. You'll find this information in your vehicle repair manual. Using a torque wrench saves you from many potential problems. A loose spark plug not only affects cylinder compression, but also overheats and burns, drastically reducing its service life. And an over tighten plug damages the cylinder head and leaves you with an expensive repair job.
  • Once you finish installing the first spark plug, replace the spark plug wire or coil.

Follow the same procedure to install the rest of the spark plugs.

Learning how to change spark plugs and other simple maintenance tasks is one of the best ways to keep your car in good shape. Bookmark this page and go over these tips any time you need to replace the spark plugs in your vehicle, your aunt's or a friend's car. It'll help you do the job right the first time, every time.

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