Spark plug question

Ok, my 94 Grand prix with a 3100 has a mis fire. So I pulled the wires, and noticed one cylinder wasn't firing quite right.
I pulled the plug, and cleaned it up. During the cleaning process, I noticed
that the element on the plug (where the spark shoots out during firing) WIGGLES. I mean, I can actually see it moving inside the ceramic. I checked another plug, and it doesn't do this. My question is .. should the electrode wiggle in the ceramic?
To recap, I got a plug that the element (part that shoots spark into the cylinder) wiggles. It shouldn't, correct?
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clevere wrote:

NO! All parts of the plug should be firmly attached. Does it otherwise look ok? No mashing, burning, etc. of the electrodes? Sounds like it broke internally. It was probably just a poorly manufactured plug (they can't all be perfect) or it somehow got damaged.
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Replace the plug and check into it's warranty provisions. That plug is damaged and it doesn't make sense to continue using it. But now you have to figure out WHY it became damaged...even so, just change it.

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Thanks guys, I knew that wasn't right, but I wasn't 100% sure .. (sounds wierd huh). Anyway, otherwise the plug looks normal, except for the electrode part, instead of being flat, it's a little rounded. Almost like it got a little hot. Kind of like the picture at this link:
www.mztech.fsnet.co.uk/ images/plugs/plug9.gif
except it's overall condition is a hell of a lot better. The only portion that looks similar is the sounded head of the electrode (instead of being flat). The length of the electrode looks fine, and the ceramic looks ok, so I don't think the piston it it. Maybe the gap was off? I've NEVER in my life had a plug wiggle like this...

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Clevere if the center electrodes of your plugs look rounded like that you are way overdue for a change. You most likely need new wires as well. Go get some new plugs and wires. Stay away from bosch and champions, Autolites and ac delco's are good. Check your new wires with an ohm meter to make sure they are good (yes new wire sets are known to have bad ones). Just to be sure you know that if you have to pull a wire back off only pull from the boot. If you pull on the wire you will damage it.

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The plugs and wires are less than 1 year, or 15k miles old. So I'm not sure what in the hell is causing that problem. I will check the wire when I replace the plug tonight. Thanks for the tip!

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how many ohms should a good plug wire read???

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WHO?? wrote:

Less than 15k. 5k to 7.5k would be very nice. 11k is still ok.
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In general conventional plug wires have a resistance of 10,000 to 15,000 ohms per foot of length. For cables less than 25 inches in length, resistance generally should not exceed 30,000 ohms. For those over 25 inches in length, the maximum acceptable reading is 50,000 ohms. Specifications vary with car makes so checking with your service manual is a good idea. If you run platinum plugs you might want good low resistance wires because Platinum plugs in of themselves have a higher resistance than a plain copper plugs. Usually none of my new wires I use go above 5k ohms and I return them if any read over 25k-30k ohms. Returning wires are easier than dishing out money for replacing a damaged coil. When installing new plugs its not a bad idea to use a very "thin!" coating of high temp anti-seize compound near the top of the plugs threads. I say top because people sometimes get a glob of anti-seize on the electrodes and then that plug becomes fouled...

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I replaced the plug, life is good and the GM engine is firing on all cylinders again. Plug wire checked out at ok also. I have no idea why that plug was screwed up, but I'm going to watch that cylinder and part of the coil pack for continued problems.

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Spark plugs are like anything else. They can fail. Ever notice in a Winston Cup race when I car loses a cylinder because a plug wire blew off? Plug wires have no reason to blow off if they are installed properly. What really happens is the same thing you had a problem with, the center electrode was poorly bonded to the ceramic and the extreme cylinder pressure in a Winston Cup engine leaked out through the plug and thats what blew the plug wire off the end of the spark plug. In your street engine with lower cylinder pressures all you ended up with was a misfire.
The price or perceived quality of the brand of the plug has little to do with the failure. Every so often someone will end up with a defective one.
-- Mike.................................................... "Opportunities are spawned from crisis"

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Thanks for the explanation Rufus. I just didn't think the electrode core would break hehe. Seems to run like a top again, and the wife isn't bitching at me so. So life is once again normal as it can be.

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Thats the main thing: keep the little woman off your back. hehehe
-- Mike.................................................... "Opportunities are spawned from crisis"
Thanks for the explanation Rufus. I just didn't think the electrode core would break hehe. Seems to run like a top again, and the wife isn't bitching at me so. So life is once again normal as it can be.
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That is totally the truth

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As a friend of mine says, "Happy wife, Happy life". and, "If she's not happy, NOBODY is happy!!"

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