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Alright, after a day of working on it, I'm pretty sure that somehow one of my spark plug holes is stripped out. I'm likely going to tow it to a shop tomorrow to confirm it is dead and/or fix it if not, but wanted to see if anyone had any thoughts here as well.

2003 Mazda 6 V6

So it all started back in December when I started getting misfire codes with about 98,000 miles on the car. I had problems for the first 45,000 miles that I had the car and the dealership kept fixing it under warranty, and finally told me I was just driving too hard (hey, I'm just driving it to the fullest capapbilities it was designed to be run at when the throttle is at 100%, right? ;-) ). But I was good for 50,000 miles after I started driving a little more normally, and I didn't want to spend a bunch of money again with recurring problems. So I knew if I replaced all the coils and spark plugs, I'd be set, and if I bought quality pieces, I could replace everything for not much more than what the dealership would charge for a bandaid fix.

So I bought the sweet WeaponX coils and plugs and put them in at the end of January. It took me two days and three trips to autozone to get all the right tools to do the job right, but I was very careful and it was successful. I made sure to slowly insert the plug as straight as possible, turning very slowly and made sure not to force it if I felt the threads not lined up perfectly. Every one went in perfectly like a hot knife through butter, turned many turns as it went in until I knew and felt it was toward the end of the threads. once I felt a little pushback, I stopped immediately. The plugs had to be deep in the wells, and the coils all pushed on nicely and seemed locked in even without a screw (no screw hole on the weaponX coils like the stocks have. No mishaps when putting the car back together. The car drove like it never had and I was zooming again, very happy and proud of my successful repair. No more check engine lights.

All was great until yesterday, about 7 weeks after the repair, when I heard a bad repetitive thumping sound in the engine as I was randomly driving at 40 mph. I especially felt it when I'd push the gas. So I pulled over after a few hundred feet when I was somewhere safe on a side road. I could see the far left coil was dislodged and was not tight at all anymore. I tried pushing it back in but it wouldn't stick. And of course it had to be on the far bank underneath the intake manifold. So I tried rigging it to get back to my house for further investigation with tools, but it kept bouncing up and down if I started the engine.

So I get it towed back to my house and take it apart today. When I get the intake manifold off and pull out the coil, the plug comes right out with it. Naturally that explains why it was bouncing up and down - the plug wasn't even in anymore. So I get a new plug and stock coil, and try to put that plug in - but it won't go in smooth like butter anymore. I try repeatedly to put it in but I would get a half turn in before it would start to lock up, so I immediately unscrew it and pull out, and try again. I couldn't get it in and had almost given up when I gave it another shot. I dropped it in with the socket, and start turning - and it turns like butter again - but for what seems like forever, longer than before when I put them in. Eventually I feel some pushback, and I figure it's in good finally. Put a stock coil on (one with a screw, the weaponX ones have no screw), and put everything back together again. When I try to start the car again - I hear a loud pop and the plug shot out again. When I take it apart again, and pull out the coil, the plug pulls out with it.

So that's where I stand now - I can see down in the cylinder but can't really tell if it looks screwed (or threaded!) or not. I have no idea how the plug could just "come out" after 6 weeks - I used anti-seize compound and know all plugs turned about the same amount. Any thoughts on how this could happen, anything I could have screwed up, or if there is a prayer that my engine isn't shot? I'm taking it somewhere tomorrow, and have already started looking at new cars. Any reassurance that it will be ok in the end or should I keep looking at new cars?

Many thanks in advance for listening to my story... will provide any more details or pictures if that could help.
 

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Quick update - I just looked at the spark plug again and it had to have been screwed all the way in. All the anti-seize compound was pushed out of the threads and the plug was clearly flush, you can tell from looking at it that it had to have been screwed in all the way. How is it possible for an engine to shoot out a spark plug like that?
 

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Heli Coil makes a kit to repair stripped spark plug threads. If all else fails you could always replace that head. Barring that your plug didnt do any damage to your piston.GL

 

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Called in the experts at the shop and they also said it could be fixed with a heli coil insert. I think I'll have the pros do that and it's being towed in now. Many thanks!!!
 

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Called in the experts at the shop and they also said it could be fixed with a heli coil insert. I think I'll have the pros do that and it's being towed in now. Many thanks!!!
DON'T heli-coil it!!!!!! Sorry I just read this post or I would have responded sooner. I had the exact same thing happen to me, except my spark plug blew out around 15,000 miles after it had been changed. I too towed it into a mechanic and had them heli-coil it. They charged $180, and 400 miles later the spark plug shot out again (no warranty with a heli-coil, so I was out $180). You may get more mileage with your heli-coil than that, but I promise you your best option is Time-Sert. I bought a time-sert kit and repaired it myself. It has been 3,000 miles since I did the repair and I have had 0 issues. Time-sert is the absolute best thing you can do, it is much better than a heli-coil. If you change your mind, PM me I still have my kit including an extra insert, I can rent it to you for dirt cheap.
 

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heli-coils work fine.

I don't know why your's failed but I worked in a shop that did a LOT of Cadillac 4100s and 4.5 V8s. Over a short amount of time the factory installed head bolts will pull the threads straight out of the aluminum block. We would heli-coil it and that problem would be permanantly solved.

Of course the timing covers would still warp, cam bores would be destroyed and all the other HT4100 problems would still surface but the heads would stay bolted down.
 

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heli-coils work fine.

I don't know why your's failed but I worked in a shop that did a LOT of Cadillac 4100s and 4.5 V8s. Over a short amount of time the factory installed head bolts will pull the threads straight out of the aluminum block. We would heli-coil it and that problem would be permanantly solved.

Of course the timing covers would still warp, cam bores would be destroyed and all the other HT4100 problems would still surface but the heads would stay bolted down.
I have heard alot of good things about heli-coils. Maybe the mechanic was a dumb ass and just didn't install it properly. But I do know the time-sert kit I purchased is worth its weight in gold. The tools are solid and it's very easy to do. Hopefully the heli-coil will work out just fine.
 
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