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What You Need To Know About Spark Plugs

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Hi, I'm Mike from 1A Auto. I'm here to talk to you a little bit about spark plugs. I've got a brand new plug, and I've got a used plug out of a vehicle. What I want to talk about is spark plug wear.

Now, what is a spark plug? A spark plug provides a small electric spark to ignite the fuel that runs in your engine. Basically, it goes into your engine. The spark plug wire or coil plugs into the top, and then this is threaded into the head of your engine. A pulse comes from here, travels to the diode, and then a small spark goes between the diode and this tab down here. This diode and tab are a certain distance from each other, so just to point them out, here's the diode and then the tab is the very bottom part.

I'm just going to flip them the other way here. The diode and tab are a specific distance from each other to provide the best spark, and that distance is different in different vehicles. Happens to be the 2008 Dodge Ram that's behind me, and the specification is .040.

If I take the .040 gauge, it goes through there, actually, probably just a little bit too easy, so I'll take my gauge and bend this tab down to close that gap a little bit. Then the .040 gauge goes in, little bit of pressure. I just work it through and then it goes through with just a little bit of resistance.

On my old plug that I pulled out of this vehicle, the .040 gauge, shoo right through. Actually, I can go to, let's see, let's try .060. It's actually set to about .060, even that goes through pretty easily. This tab is about 50% larger than it should be. That's what happens when plugs wear. You can see the distance on the old plug between the diode and the tab is a lot larger. You can also see that the diode itself is worn out and that the tab is worn out some.

What will happen eventually is each time a spark goes between here, a little bit of the diode and little bit of the tab wears away. It'll get so large that the spark won't be able to travel and you'll start having misfires.

Something can get onto the spark plug which prevents the spark from traveling. That's what happens when your spark plug gets fouled. A spark plug can be fouled by too much fuel. It can be fouled by dirt and contaminants, but, here, like I said, we have a worn spark plug and that's what can happen. The thing with iridium spark plugs, the newer technology, the iridium just is more resistant to that wear, so they tend to last longer. If your car has anywhere from usually the older style plugs, maybe every 10,000 or 20,000 miles, iridiums are now 100,000 miles. It's pretty obvious that in this Dodge Ram we need to change the plugs.

Thanks for tuning in. We hope this video helped you out. Next time you need parts for your car, please visit Also check out our other helpful how-to and diagnosis videos.

Tools needed for replacement:

    Specialty Tools

  • Spark Plug Gapping Tool

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