Bad fuel injector ?? / 08 excalibur

[shag]

08 343 excalibur motor with 1100 well maintained hours. No salt use ever.
Recently having hesitation and rough idle with black smoke at idle.
Just did a PM which included new fuel filters, recommended plugs, cap and rotor, plug wires, oil and filter change. (even bought a second cap to try to be sure I didn't get a bad one).
Still having same problem and after going one by one on the new spark plugs (replacing with a new one to be sure I didn't get a bad one) I find one cylinder with a white basically looks un used porcelain. Other plugs are light black to dark brown. Apparently that cylinder was on the compression stroke when Removed the plug as I got a strong hiss of air when I loosened the plug. (engine hadn't been run since Sunday (24 hours). I don't have a compression tester.
Small dash temp gauge stopped working around same time but digital display in tach reads normal temp when warmed up (150-160). Dealer says as long as digital gauge works that it is not the problem.
Has anyone ever had an injector go bad on one of these?
No codes stored when engine checked (not running).
Anything else? I'm stumped and took it to the dealer ..Sadly hourly rate is near $150

[8urchvy]

I had a rough idle and replaced all plugs, wires , cap and rotor. I had a bad plug. But the tune up didnÂ’t fix it.

I think itÂ’s a bad valve. Low compression in that cylinder. That seems to be what the symptoms indicate.
2007 343 only 250 hours.

You need to do a compression test.

Good luck.

[shag]

Thats interesting, Now that I go back and look at the plugs I took out the first time, that cylinders plug is missing the electrode as well... Dang.. Can't believe I didn't notice that.. The electrode is so tiny on these plugs anyway.... Man that sounds like an expensive repair... Just what I don't need...

[8urchvy]

My plug was loose too. I’m not sure if the loose plug caused the arching and that ruined my plug and then the plug wires and the valve. I haven’t torn it apart yet but will need to before summer. Ugh.

[shag]

Yeah weird... I could see a loose plug causing the detonation of the plug due to irregular conduction... Hopefully the tiny debris made it unscathed out the exhaust

[H2O]

Usually, detonation causes the plug to become loose not the other way around. Extreme detonation could also blast the plug enough to break it apart. I would try to figure out why there was such severe detonation in that cylinder.

[shag]

Just an update. No compression in #3 cylinder, dealer pulled head and found "mushroomed" valve (going to have a look today)... Not exactly sure what they're describing but sending head to machine shop to be repaired... Estimate around $1500 parts and labor total... Of course most of that is labor...
Everything else checked out fine.. Cylinder and piston fine, and all other cylinders in good shape with excellent compression.