Piston/ Something Hitting Spark Plug???
 

Ok so I'm a brand new member. Pretty sure I searched enough and couldn't really find anything about this. I did find one thread from a few years ago but they didn't really address the cause of the problem. A little back story. I have a 2007 Cobalt ss/na 2.4L. I left my house one morning and drove about 2 miles to school. The car ran fine almost the whole way until I went to pull into a parking spot and it started sputtering. I didn't think much of it until I got out of class and it was still missing except worse. I limped it back home and got a code reader and it was throwing a code for a missfire on cyl. #2. So I pulled the plug and the grounding pin and electrode tip were both gone.

I never heard any knocking or engine noise whatsoever. Inspected the cylinder as well as I could and there's nothing in it. So I replaced the plugs just to see if it would still run and it ran great for the last week, until yesterday when I really laid into the throttle and almost instantly it went into limp mode and started missing again. Pulled the same plug and the grounding pin is bent over touching the electrode! I know I've got the right plugs, compression is 155-160 across the board, without pulling the head and without having a borescope, I'm as sure as I can be that there's nothing floating around in the cylinder and I have no idea what could be causing this. ( I have some ideas but none of them seem plausible) I feel like a new engine/ rebuild is inevitable at this point but this just doesn't seem possible.

The car has 165k on it and I've had head problems almost exactly every 55k miles. Head gasket replaced under warranty at 55k and the head replaced at 110k. GM claimed that there was a TSB on the valve seats and they covered 2/3 of the repair. I was almost prepared to have head problems again as I hit the next 55k mile marker but this has me baffled. Any help is appreciated, hopefully there aren't any threads about this that I missed. Thanks

How long have these exact plugs been run before this happened? I've seen some really bad carbon buildup but doubt it would do this.

Take off the intake manifold and shake it. This exact thing was happening to me and i couldnt figure it out. Took off the intake and the top conpression ring was in a million pieces inside of it, so everytime i got on it, pieces would get sucked back into the cylinders.

I'll take a look at that thanks

The first plugs were about 20k miles, I already had new plugs because I was getting ready to change them but they weren't super old. But the second time the plugs were brand new, and it happened on the same cylinder

Got my Amazon bore-scope in and once the rain let up i went out and took a look and nothing. Cylinder and piston looked fine! Gonna check everything over again tomorrow and If I can't find anything else I'll have to throw another plug in it and try again....Anybody else have any advice??

What plugs are you running?

They're the OE delco plugs.

I'm seeing 3 ACDelco plugs on RockAuto, is it one of these?
ACDELCO 17 Professional; Rapidfire
ACDELCO 41834 Professional; Double Platinum
ACDELCO 41103 Professional; Iridium

Just trying to narrow down the possibilities.