starting to look worse and worse...
this was an almost new plug when I put it in last evening just before dark, the truck has only been run for maybe 15 - 20 mins since then.
what is that deposit of stuff at the end ?
almost looks like carbon buildup ?
not entirely sure.

as you can see though, the entire thread piece to the end is pretty burnt.
also, the crack in the ceramic that wasnt there before.

 

looks like its running lean

 

I havent a clue at this point, hell, my mechanic also doesnt understand.
simply removing a spark plug and putting a new one in shouldnt be giving these results, especially if the plug replaced was the one giving the problems....

Ive gone through all my wires, they are all seated good n tight, checked the coil and Im getting good spark from all points, ran a code scanner on it and came back clean, but its still running like on 5 cyl.

there is a slight amount of water coming from the tail pipe, but its nothing more than it always had, but there is a strong smell of carbon monoxide coming from the exhaust, no backfire, from either exhaust or intake. Im simply at a loss...

 

have you checked the compression on that cylinder it sounds like you have a blocked catalytic converter or a bad fuel injector

 

Im setting up to get a compression test in the next few days.
but I also think (hope?) it might be the cat, as far as I know its the original which means it has 170k on it.

Ive been going and going over it and I still simply cant understand how changing 1 plug could cause this much mayhem. even though it could have been something that has been building up, it really was so sudden. I mean, Friday, I drove the truck from Sebring down to Miami and back and it ran great, no torque loss, got decent mpg (on the way down), then 2 days later I change a single plug and now... this.
something else I should mention, but I dont really think has anything to do with it, but it might, is the plugs in the truck are motorcraft, but since I cannot get motorcraft parts anywhere near me, I got an Autolite plug. that said, the old plugs from a few months ago were autolite. my mechanic said its possible that it could be a bad plug, he says he has seen that a few times.
or that having two different brands could have an affect, but I do have a hard time believing that, but I guess anything is possible.
*shrugs*

 

final update....
ok, so either its just my dumb luck, or I simply have to take the hard route....

anyways, I finally found the problem.
the new plug was bad, the old plug was bad, and the other plug I tried was ALSO bad.
out of 4 plugs I tried, only 1 was good...

so anyways, so far so good, my truck is running great as it ever has :)

 

Have you been able to check if the misfire is coming from one cylinder consistently?

 

no misfires anymore, Im thinking the original problem was due to a slight crack in the ceramics, then the new one I replaced it with was bad, and the new one after that was ALSO bad. (with a loose post, ceramic was undamaged)
Im hoping Ive resolved this, but I'll will still be putting it on a diagnostics computer soon, maybe within the next two weeks.

when I do, I will post back with info.