How to Gap a Spark Plug?

Reviewed by

Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Written by CarParts.com Research Team - Updated on March 18th, 2024

Reading Time: 4 minutes
Summary
  • An incorrect spark plug gap can result in poor fuel economy and engine performance.
  • The appropriate spark plug gap is dependent on your vehicle’s specifications. Be sure to consult your owner’s manual to get accurate information.
  • There are three types of spark plug gauges that you can choose from when trying to gap a spark plug. These are the coin, wire-coin, and blade-style feeler types.
Diagram showing spark plug gap | Image Source: Richard McCuistian

Gapping your spark plugs is crucial as it affects the combustion event in the cylinder it fires.

A gap that is just a bit too close causes random misfires at idle but won’t usually cause issues you can feel while driving. A gap that is just a bit too wide is actually better for starting and idle quality but uses a bit more coil energy, which doesn’t hurt a thing unless you crank the engine up to the red line regularly (which isn’t a good idea, by the way).

There are caveats to gapping plugs, one of which is that some spark plug gaps are fixed and don’t need to be changed. One example is the 5.4 3-Valve Ford spark plug as shown in this photo. | Image Source: Richard McCuistian
There are also plugs with multiple electrodes that don’t need to be gapped, such as is shown in this photo. | Image Source: Richard McCuistian

Truly—and we can’t stress this enough—proper gapping is key. So, how do you do it? Here are three easy steps.

A gap that is just a bit too close causes random misfires at idle but won’t usually cause issues you can feel while driving. A gap that is just a bit too wide is actually better for starting and idle quality but uses a bit more coil energy, which doesn’t hurt a thing unless you crank the engine up to the red line regularly (which isn’t a good idea, by the way).

Richard McCuistian, ASE Certified Master Automobile Technician

Step 1: Gather the Things You Need

Start by finding your ride’s gap specification. Keep in mind that spark plug gap dimension depends on the engine type of your car. Take note, too, that every car’s engine is different and unique from each other so be cautious in choosing the right gap dimension to use. Now, if you are anxious when it comes to reading spark plugs, it’s best to check your car’s manual. Or, you can ask assistance at your local auto parts shop for a more precise dimension.

To ensure that you have the accurate measurements, you can also check the spark plug cross reference chart. This reference chart is available online so accessibility is not a problem.

After checking the required dimension, the next thing to determine is the spark plug gap gauge to use. There are three kinds: the coin-style gauge, the wire coin gauge, and the blade-style feeler gauge. Use the gauge you are most comfortable with.

Step 2: Examine Your Spark Plugs

The condition of your spark plug is of utmost importance so be sure to examine and remeasure each of your newly-bought spark plug replacements before using them. If you are remeasuring your old spark plugs, make it a point to clean them first and check them for are any cracks or bubble formation.

You can refer to your spark plug chart so you can be aware of the exact condition of your old spark plugs. It ranges from normal to normal with red coating, fuel fouled to ash fouled, and overheated to worn out.

After that, measure each spark plug by passing the gauge between the electrodes. See if adjusting is needed. If the gauge passes through the electrodes quite smoothly, the gap is too wide. On the other hand, if the gauge can’t fit between the electrodes, the gap is too narrow.

Step 3: Adjust Accordingly

After knowing the current gap measurement of your spark plugs, you need to adjust the distance between the electrodes according to your engine’s requirement. Gauges nowadays feature a specific edge for bending your ground electrode. Use it to adjust the gap by gently bending the ground electrode down to narrow the gap and by tugging it up to widen. Repeat the process until you reach the required gap for your spark plugs.

Where to Get High-Quality Spark Plugs for Your Vehicle

While gapping a spark plug is crucial in maintaining its functionality, it won’t work if the plug is bad. In this case, the only solution is to look for a replacement. Fortunately, high-quality spark plugs aren’t difficult to find when you shop at CarParts.com!

We offer an excellent array of quality spark plugs at unbeatable prices. To ensure they’ll perform like your stock parts, we ensure that all our spark plugs pass the highest quality control standards from industry professionals. We also source our products from trusted and well-known manufacturers to ensure you get your money’s worth.

Simply fill out our vehicle selector and use the search filters to find the right spark plugs for your ride. If you have any questions, don’t hesitate to contact our customer service team via our toll-free hotline.

Take care of your vehicle’s ignition system. Shop for high-quality spark plugs today!

About The Authors
Reviewed By Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Written By CarParts.com Research Team

Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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CarParts.com Research Team and Richard McCuistian, ASE Certified Master Automobile Technician
Tags: spark-plug