How To Gap a Spark Plug

Mind the gap!

Fouled spark plugs need to be replaced.
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Though the entirety of your car’s movement depends on your spark plugs working perfectly, they’re one of those car parts that people often overlook, forgotten and unloved. That shouldn’t be the case, especially considering inspection is simple and straight-forward. One of the easiest ways to show your attentive appreciation is gapping them correctly.

A spark plug’s gap refers to the space between the center and ground electrodes. Taking the current provided by the car’s battery, the center and ground electrodes produce a spark that ignites the car’s fuel and air mixture. Without it, you ain’t gettin’ anywhere. Time, then, to learn how to gap your spark plugs!

Don’t worry if you’re still a garage noob because The Drive’s crack info team has your back. So let’s dive into what spark plugs are, what they’re made of, and how to properly gap them. Ready?

A spark plug.
Depositphotos

A spark plug.

What Is a Spark Plug?

Spark plugs are an engine part that ignites the fuel/air mixture through a small spark between two electrodes within an internal combustion engine. As atomized fuel and air enters the engine’s cylinders, the spark plugs at the top of the cylinder ignite combustion. The spark plugs are connected to the vehicle’s electrical system through spark plug wires.

Different spark plugs utilize different materials, the most common being nickel, iridium, copper, and platinum. Manufacturers also use a small piece of ceramic as an insulator on the spark plugs.

Common Spark Plug Problems

Like any car part, spark plugs can go bad for a host of reasons. Here at The Drive, we’ve broken it down to easy-to-understand terms and outlined the most common spark plug issues. Ready to get schooled?

  • Incorrectly gapped spark plugs could cause engine misfires.
  • Corroded spark plugs could halt the spark altogether and, again, cause misfires.
  • Broken spark plugs could, you guessed it, cause misfires AND if pieces of the ceramic enter the cylinder, could cause far worse issues down the road. 
  • Improper timing or incorrect gaps could also cause engine knock. Read The Drive’s guide, “What Is a Knock Sensor?” for more information.

Spark Plug Basics

Estimated Time Needed: 1-2 hours

Skill Level: Intermediate

Vehicle System: Engine

Safety

Working on your car can be dangerous and messy, so here’s exactly what you’ll need to ensure you don’t die, get maimed, lose a finger and keep your jeans, shirt, and skin spotless—hopefully.

A spark plug gap tool.
Depositphotos

A spark plug gap tool. 

Everything You’ll Need To Gap A Spark Plug

We’re not psychic, nor are we snooping through your toolbox or garage, so here’s exactly what you’ll need to get the job done. 

Tool List 

Parts List 

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won't need a blowtorch for this job. Please don’t have your kid hand you a blowtorch—Ed.)

You’ll also need a flat workspace, such as a garage floor, driveway, or street parking. Check your local laws to make sure you’re not violating any codes when using the street because we aren’t getting your ride out of impound.

Here’s How To Gap A Spark Plug

Now that your garage is organized and you’ve read our safety disclaimer, let’s do this!

Before ever touching the new spark plugs, you’ll need to find what gap your car’s spark plugs require. You can also remove the old spark plugs and use the spark plug tool to determine its gap, though they may be out of gap too. You can compare three or more to see if there is a standard gap between them. You can also use your car’s dusty, old manual. Once you have the right gap, you can then get to gapping the plugs.

  1. Insert an OBD ECU memory saver, if necessary.
  2. Disconnect the positive battery terminal. 
  3. Take the first new spark plug and insert the gap tool between the center and ground electrodes of the spark plug.
  4. Slide the gap tool between the two electrodes and increase the gap with light pressure. 
  5. If you need to decrease the gap, gently squeeze the electrodes together or very lightly tap the spark plug on a towel on a table. 
  6. Double-check the gap size. If it’s right, perfect. 
  7. You can now “rinse and repeat” for all the other new spark plugs.

That’s it, you’ve done it!

A set of bad spark plugs.
Depositphotos

A set of bad spark plugs.

Get Help With Gapping A Spark Plug From a Mechanic On JustAnswer

The Drive recognizes that while our How-To guides are detailed and easily followed, a rusty bolt, an engine component not in the correct position, or oil leaking everywhere can derail a project. That’s why we’ve partnered with JustAnswer, which connects you to certified mechanics around the globe, to get you through even the toughest jobs.

So if you have a question or are stuck, click here and talk to a mechanic near you. 

Pro Tips To Gap A Spark Plug

Throughout the years, The Drive’s editors have gapped dozens of spark plugs. We’ve picked up a few tricks from those experiences and we want to impart our learnings on you, our padawans. 

  • Some spark plugs come pre-gapped for your car. You can check the box and save yourself some time. 
  • Incorrectly gapped spark plugs will cause misfires. Double-check your work. And if you’re still unsure, you can either ask JustAnswer or call your local auto parts store for help.
  • Get a spark plug socket wrench. They’ll save you time, broken knuckles, and ensure that your spark plugs don’t break during removal or insertion. 

FAQs About Gapping Spark Plugs

You’ve got questions, The Drive has answers!

Q: How Much Does It Cost To Gap a Spark Plug?

A: Gapping a spark plug only costs you the price of the gap tool, which is, at most, $4-$5. 

Q: Why Do You Need To Gap a Spark Plug?

A: As we’ve illustrated above, gapping a spark plug ensures your car’s combustion cycle remains consistent with factory specifications. This then ensures that your engine remains healthy and happy. 

Q: What Happens If You Don’t Gap Spark Plugs?

A: Ungapped spark plugs will cause misfires as the gap between the electrodes could be too small or too wide. The air/fuel mixture then may not ignite or ignite on the wrong stroke, which can cause misfires.

Q: What Happens If Your Spark Plug Gaps Are Too Small?

A: Similar to ungapped spark plugs, if your gap is too small, the resulting spark may be inadequate to ignite the fuel/air mixture and cause ignition. 

Q: Do Spark Plugs Come Pre-Gapped?

A: As mentioned, some do come pre-gapped! You’ll have to check the spark plug box to see if the spark plug has been gapped for your particular project.