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I have a 454 engine in my cabin cruiser boat. After operating at normal cruising speed for 20 minutes or so a spark plug was blown out of the engine, with the center electrode melted, and the rest of the plug left in place. I replaced that plug, checked the others and they were fine. The next time out, the same cylinder, brand new spark plug blew out again, same deal, melted electrode and the whole center of the plug blown out of the engine. It has a mercruiser electronic ignition. Any Ideas??

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    If you could post a picture of the aftermath of one of the sparkplugs, it would probably help (maybe a couple of shots of it so we can see the electrode which was melted, as well as the parts which were still in the head). – Pᴀᴜʟsᴛᴇʀ2 Sep 7 '15 at 23:15
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    Any chance water is getting into the exhaust manifold, due to poor risers or exhaust port flapper seals? – Fred Wilson Sep 8 '15 at 4:35
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    @FredWilson - If it were to get water into the cylinder, it would prevent detonation, not cause it. Water injection systems in effect raise the octane rating of fuel by about 10 points. Besides, considering the exhaust valve is only open during the exhaust cycle, I doubt you're going to get water into the cylinder with all of the exhaust gases trying to get out. – Pᴀᴜʟsᴛᴇʀ2 Sep 9 '15 at 0:55
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    @vini_i - That's kind of what I was thinking. If the engine is port fuel injected and the injector for that cylinder was not allowing the proper amount of fuel, you'd have an extreme lean condition in that cylinder, which could cause severe detonation. About the only way I see what is being described as happening. This theory would be shot to crud if it's carbureted, though ;-) – Pᴀᴜʟsᴛᴇʀ2 Sep 9 '15 at 0:57
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    @verncarpenter It's possible that you have a collapsed lifter on that cylinder and the heat cannot escape. It's a reach, I know, but I have seen this before. have you noticed and strange sounds emerging from the engine? – DucatiKiller Dec 17 '15 at 5:22

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