Ok so my son just bought a 2015 with Boost it turbo and I have a backfire on a climb and just runs ****ty most of the time I am thinking it’s nothing to do with turbo but may be wrong. On a pull at about 7800 rpm it starts to lose power and then backfires. I have fresh fuel in it checked over everything I can think of.Also the y pipe is a gross yellow colour inside .Just bought the sled and not likely gonna get the real story from past owner. Is this possible just a bad plug or weak coil. Any help would be really appreciated