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2003 Civic LX @55K miles.....
Started with flashing CEL. Other 3 plugs looked ok (top picture/top plug).

Any ideas what could cause this? What to check? Thanks...

 
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Preignition

Symptoms:
Melted electrodes, Insulators are white, but may be dirty due to misfiring or flying debris in the combustion chamber. May lead to engine damage

Reccomendation:
Check for the correct plug heat range, overadvanced timing, lean fuel mixture, insufficient engine cooling, and lack of lubrication



Detonation:

Symptoms:
Insulators may be cracked or chipped. Improper gap setting techniques can also result in a fractured insulator tip. Can lead to piston damage

Recommendation: Make sure the fuel anti-knock valves meet engine requirements. Use care when setting the gaps on new plugs. Avoid lugging the engine.


This is from my Haynes manual. From what I can tell, it can be either of the 2. Post more pictures of the bad plug, large pictures from different angles.

 
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I'll post more pics tomorrow.

 
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ya please do, im curious to see more

 
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Here's more pics:

 
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This is off topic, but those are great zoom pictures, what camera are you using?

 
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Most cameras with a macro setting will let you get that kind of detail.

Anyway, I'll bet dollars to donuts your flashing CELs are misfire codes. And yeah, holy ****ing detonation Batman. I'd change out that coilpack and get your CELs read to see exactly what's going on. That ain't good man.

 
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Old Canon PowerShot SD200 3.2MP.
Pics were taken with Macro ON...

 
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Definitely doesn't look good. You were right about misfire codes.

Replaced the coilpacks (OEM) and the plugs with Denso Iridiums.
No CEL as of yet. Still have to pull the plugs out to recheck 'em...

 
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May want to do yourself a favor and get a compression test done on the car (should be no more then $40-$50) to make sure nothing else got damaged from the detonation on that cylinder. You run the risk of having the head lift from severe detonation (popping the HG) and/or blowing a ring on the piston as well.

 
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Looks like oil getting into the chamber, try replacing your Spark Plug Seals... this will require you to remove the valve cover and possibly change ur valve cover gasket at the same time.

 
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Yep, that's exactly what he's getting. The spark plug tube seals have dried out and this is letting oil seep past, down the plug and into the combustion chamber. It's a common Honda problem (especially if you're running too lean somehow). I got the same problem on my #2 plug but it's not bad enough yet to throw a CEL. Every once in a while I get a mildly uneven idle (slight miss). I usually just pull the plug out and clean it or put a new plug in. To fix it correctly, all you need to do is replace the spark plug tube seals, which means replacing the valve cover gasket as well. It's an inexpensive fix but involves a little labor. (Enough labor that my lazy *** ain't prepared to do yet!!!) LOL

 
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Thanks guys.
Friend of mine who's mechanic said the same thing, to try spark plug seals first.

Will order a Gasket Set (12030-PLC-010), Both, plug seals and valve cover gasket should be included if I'm not mistaking.