How to Test Spark Plugs

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When testing spark plugs, make sure that all of the fuel pressure is out of it so that fuel doesn't get dumped in the rail. Use a spark plug checker to check for a spark with help from a certified master mechanic in this free video on car maintenance.

Part of the Video Series: Car Maintenance
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Video Transcript

Good afternoon. My name's Tom Brintzenhofe, a certified master tech out of Redding, PA, and today we're going to talk about how to check your vehicle's spark plugs. How to test your vehicle's spark plugs. Now the first thing you want to keep in mind if you're going to go out and test your spark plugs on your car, the last thing that you want to do is be cranking this engine, and have that fuel being dumped into your....into each cylinder, only it's not being burnt off. It's not real good for your cylinder walls, your piston rings, and it's definitely not good for your oxygen sensors and your catalytic converter, so that's one thing you want to avoid. And by doing that, you could either pull your fuel pump fuse, or your fuel pump relay. Start the car, if it does run, or just crank it for awhile. Just make sure all the fuel pressure's out of it, or it can...if it does run, just so that it runs 'til it runs out of fuel. 'Cause that's the last thing you want to do, is dump fuel in the rail, I mean dump fuel into your cylinders. Well, what you want to do is take your spark plug wire off. Just twist it counterclockwise, clockwise, and just give it a little pull and yank it off. You don't want to damage your spark plug wire. Take your spark plug on out, here. You want to keep your hands and everything out of the engine compartment if at all possible, you can get an extension on it that comes out and clears it. It's better than working in here and smashing your knuckles. If you can get away with it, it's better to work out here than working down inside, here. Pull your spark plug out, put it back in your spark plug wire, and this normally takes two people to do, 'cause you're not going to be able to see this from the inside of the car when you're cranking it. You're going to have to have somebody watch this, here. And hopefully you'll be able to see what's going on. I'm going to lay it up here on the intake, if I can get it in position, here. It's gotta be touching metal, it cannot be on plastic at all. It's not....just not going to work for ya. But, get it laying there on metal. And what you want to do is you want to crank it a little bit. Now, if you see a spark or even just a weak spark, and you might think the spark plug's at fault, they make tools out there. One's a spark plug checker, and it checks and makes sure you have enough available spark to fire this spark plug. If, by any chance, you think this is weak by any chance, get yourself one of these. They cost four dollars at a local parts store. And, again, it's gotta be touching on metal when you crank it. And when you do this, you can do this by yourself, you'll actually hear it. It'll be like a little snapping noise. Hopefully you'll be able to hear it from your end. Ready? And that's about all there is to checking a spark plug. The only other option you have when looking at a spark plug is to make sure you don't have any build-up in here, whether it's gray or black, covering this porcelain or this tip right up in here. Those are your two main areas. If you get a lot of build up in here, there's a lot of chances these won't fire right. And this gap right here has got to be set. Now this is always printed right on your front label. If you have a label that's still readable on your car, just go ahead and read it. A spark plug gap is .060. Lot of the parts stores will have a...there's a tool for checking 'em. It costs, like, two dollars to pick one up. But just make sure your gap is where it needs to be, and that's the gap between your electrode and this little arm sticking up in here. But once you get that all there and it's nice and clean like that, that's a good spark plug if you can hear it sparking the way it did earlier. And that's about all you need to do in checking a spark plug.

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