How to Identify a Bad Spark Plug

Part of the Video Series Changing Spark Plugs

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Why is my car not starting? Learn how to identify a bad, or fouled spark plug in this free online instructional video.

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Video Transcript

How to Identify a Bad Spark Plug
Hi, this is John from Expertvillage.com. In this video clip, I will talk to you about what a foul spark plug is. A spark plug is considered to be fouled when the insulator knows that the firing tip becomes coated with a foreign substance such as fuel, oil or carbon. So here I have a new spark plug and the insulating tip in the center is clean, and looks really good. Here I have a foul spark plug and you will notice that the insulated tip has a quite bit of oil and other items on it and this may have been a clear cause of why this spark plug became fouled. When a spark plug becomes fouled such as this one, it dramatically decreases engine performance and will reduce fuel economy. A good way to fix that is to either replace your spark plug or you can take them out and clean it as I will show you in the clips ahead.

About the Expert

Expert: Jon Olson holds a Bachelors of Science in Education and Human Sciences degree, with an endorsement in Industrial Technology Education from the University of Nebraska in Lincoln. Read More