ok, so i was working on an STi at work today. the owner was driving last week and it got a random misfire. so he drove it home and brought it up to the shop. we change the coil based on the misfire code in the computer. it runs a little better so we change the pkugs too. the one that had the misfire had zero gap on the electrode. t looked like something pushed it in or maybe it melted. so we changed the rest of the plugs and put it back together.
now here’s the weird part. we drove it afterwards and it ran perfect. about an hour later, we go to drive it again, start going up the road, and a loud pop is heard from the exhaust and the misfire starts again.
if anyone has any idea what this could be besides a bad cylinder, please hit me up.
i think there is a hole in the piston. when we crank it and you put your hand over the oil fill, you can feel pressure as the motor turns over, plus there is a gas smell inside the crankcase.
subaru tech is going to stop over and check it out monday.
but why would a cracked ringland smash the plug? i pulled the plug out again and it was smashed even worse this time. blew the cylinder out with an air gun and metal shavings came out. i’m pretty sure the piston has a hole in it now.