VERY Weird Misfire Issue

[insite]

ok, here's the story. driving the other night, i heard a funny metallinc rattle followed by the immediated development of a misfire. i read pulled the codes; the ECU was indicating emissions related misfires on #2 and #6. i pulled the coils & let them cool to room temp; then i measured the resistance across pins 1 and 15. they both read in the neighborhood of .5 ohms, so they're within spec. visually, they looked fine.

next, i pulled the #6 plug. it looked okay; cleaned & reinstalled. now here's where it gets interesting: i pulled the #2 plug and ALL FOUR electrodes are GONE. other than that, the plug looks normal. postponing the obvious question of how this happened, i installed a new plug and everything ran great......for a few hours. now the car appears to be developing the same issue.

does anybody have any idea what would cause this? never seen this problem before. BTW, the plugs are Bosch Platinum R4 and are about 50k miles old. i haven't had a chance to pull the plug back out, but i'm thinking i might find the same thing......

here's a pic:

[insite]

ok, so i'll take a crack at it. my misfire event yesterday (after replacing the spark plug) was intermittent. now, it doesn't seem to be happening at all. i checked the codes; same ones as before. here's my theory:

the damaged plug was the RESULT rather than the cause of the misfire issue. perhaps the car was misfiring for some other reason and a turbulent misfire stripped the electrodes from the plug. my best guess as to the cause would be the coil pack (even though it tested good). as i have NO other codes, i'm tempted to just buy a set of coils. opinions? another odd thing: i could find nothing wrong with the #6 cylinder even though the OBD II code tells me this cylinder experienced misfire events as well.

any thoughts are appreciated.

[Topless]

Yup. That plug is toast. Unusual to strip away the ground electrode like that.

I see three possibilities:

Foreign object (even loose carbon) thrashing around in there. I would rent a cylinder camera and look inside #4.

Really high plug temps. As a plug wears and the gap widens it requires a lot more voltage to jump the gap. More voltage= more heat. This may have caused the plug damage and damaged the coil also.

Severe detonation. Possible but unlikely. It would have to go on for quite a while to strip the electrodes like this. You are pretty in tune with your car and I think you would have noticed this.

Let us know what you find.

[RFM]

Using the correct and approved spark plugs is the best way to go IMHO, and what with a possible cylinder liner damage as Topless stated. :o. I hope the best.

[insite]

Using the correct and approved spark plugs is the best way to go IMHO, and what with a possible cylinder liner damage as Topless stated. :o. I hope the best.

when i replaced the plugs several years ago (the car was new to me), i ordered whatever plugs they told me went with the car. looks like the bosch R4 is NOT one of the approved plugs. i ordered a six pack of Beru along with two coil packs (one for each misfiring cylinder). we'll see where that goes.