Unusual Spark Plug Question

[rblais]

Good morning everyone. Just replaced spark plugs in 2010 Mountaineer w/V8 and 59K miles. Bought the truck used at 33K. Pulled what I believe to be the original plugs and replaced with Motorcraft SP 509's; all but 7 of them anyway. When I got to the #6 cylinder there was (is) a different type of plug in it. There is no nut on this plug for the 9/16" plug socket to fit on, only what appears to be a smooth round metal ring below the ceramic as part of the plug itself. If I was seeing things correctly, there appeared to be red lettering on the white ceramic part of the plug. The 7 plugs that were removed have the normal blue Motorcraft lettering with the correct part number on them.
This engine does not have the shielded plugs that are so difficult to get out. The original plugs threaded out easily and the new ones went in easily with zinc antiseeze. Truck seems to be running fine after change out (with the old #6 plug left in place).
Does anyone out there have a clue as to what was found in the #6 hole?
Thanks in advance for any and all responses.

 

[Flag Gibby]

Don't know what to tell you, but that plug (whatever it is) needs to be replaced with a new plug. You may have to get a special tool to remove it as it sounds like the head may be stripped on it and that is why it is smooth instead of the 9/16" socket size.

 

[rblais]

Thanks for reply. The plug does not appear to be stripped or broken in any way. The metal just below the ceramic is dark in color, not black but very dark brown or bronze. The surface of the metal is smooth and rounded as far as I can tell. I have an appointment with the local ford dealer on Tuesday for front hub/bearing replacement (Drive Train Warranty I hope) and will be asking their opinion. I do want it removed and replaced with the 8th plug from the set I bought.

 

[05_moutianeer_mn]

Maybe some of the rubber boot melted on to the plug and you may need to pick it off so you may engage the socket on to the hex of the plug

 

[rblais]

You got it mn! Turns out it was a broken off piece of black rubber boot. How it got there I haven't a clue. It appeared to be metal when I looked down the deep spark plug well. I should of probed it with an awl or something similar, da! Just came back from the dealer who replaced the front hub/bearing assembly covered by the 60K/5yr power train warranty. Asked them to check out the plug and they found the rubber boot and saved it for me. Whatever it is fits completely over the hex nut on the plug, unlike the rubber grip inside the socket I was using. Anyway, if they hadn't found it I would tried your suggestion, so thanks!