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Do It Yourself - Outdoor Power Equipment Repair & Maintenance

How to Use a Spark Plug Tester

Using a Spark Plug Tester Posted in Small Engines

A spark plug tester is a handy tool that allows you to check if your spark plug is working properly. It can also save you time by allowing you to check if the problem is actually in your ignition. Follow these guidelines for an easy way to use a Spark Plug Tester.

Checking for Spark Plug Misfire

Spark plug misfire, or spark miss, is when the sparks jumping the gap of the electrodes are inconsistent in their timing. This can cause your engine to stumble, lose power, and even emit black smoke (due to unburned fuel not being ignited in the combustion chamber). The following steps can be taken to check if you are experiencing spark plug misfire.

  1. Disconnect the spark plug lead from the spark plug.
  2. Connect your spark plug tester to the spark plug lead.
  3. Connect the spark plug tester to the spark plug creating a link from the lead to the spark plug.
  4. Start the engine and watch the gap in the spark plug tester to see if there is inconsistent timing.
Spark plug tester

If you are experiencing problems, you may want to try adjusting the gap between the electrodes and trying again. If that still doesn't work, check the ignition with your spark tester, or try replacing your spark plug. Check out the selection ofspark plug we have here at Jack's.

Checking the Ignition

You can check if there is an ignition problem with your spark plug tester if it has an alligator clip at the end. This is meant to attach to the spark plug. Otherwise, you may need to get an ignition tester to move forward.

  1. Disconnect the spark plug lead from the spark plug.
  2. Connect your spark plug tester to the spark plug lead.
  3. Ground the spark plug tester's alligator clip.
  4. Crank the engine by using the rewind or electric starter and look for a spark in the tester's gap.

If there is a spark in the gap, then the ignition is working. If there is not a spark, then there is a problem with your ignition system.

Final Thoughts

Testing your spark plug can save you a lot of time and money. Spark plugs are easy and inexpensive to change. Be sure to check out our article on How to Service Your Spark Plug for some tips on how to keep your spark plug running in top shape.


Jack's Safety Tips: Before servicing or repairing any power equipment, disconnect the spark plug and battery cables. Remember to wear appropriate safety glasses and gloves to protect against harmful chemicals and debris. View our Disclaimer.