2009~2013 Extreme carbon buildup!

Hello All,

I got 2012 Mazda 3 Skyactiv 2.0 with 120k miles on it. My car recently started misfire, so I replaced spark plugs that resolved the issue but I also decided to use my snake camera inside the spark plug hole to see condition of piston, see attached pictures. Now it looks like extreme buildup but not sure 100%, i only took pictures of first 2 cylinders.

Then I decided to use CRC intake valve cleaner hoping to cleanup that gunk. It never made while smoke like other mentioned after 1 hour soak but I had mis-fire and shakes on heavy acceleration (4k rpm). Car seems to run fine and I noticed improvement after CRC but never saw this type of build-up before.

Should I worry about this build-up?


That’s a decent amount of buildup but I wouldn’t worry that much about it as you did a cleaning and changed plugs. Just keep an eye on it.
Did you do multiple cleanings and check to see the progress In between? Also did you clean this on the new plugs or old plugs. If you cleaned it on the new plugs please check your plugs as they might have buildup on them now. I always recommend doing cleaning treatments then changing plugs.
I have had cars that I needed to do multiple cleaning treatments and it definitely helped and can see the difference.
That’s nice having a snake camera as not many do. Enjoy your car.
thanks for your reply! That makes me wonder, it was maybe due to my old cheap chinese plugs. I found cheaper plugs on eBay for like $14 for 4 iridium plugs that I thought was a great deal, replaced them and car ran fine for 4 months. Recently I drove my mazda for 6 hours ride and since then it started happening, I also noticed that plug tip melted, see pictures attached.

Yes, I did multiple cleanup but didn't take plugs out to see difference but will update when I do next and I did this cleanup on new plugs. Now my new plugs are genuine NGK plugs, so hopefully that will make some difference. Will keep my eye on and will keep you posted :)