Why evertime you get something either running right in your car or you fix something, that something else decides to fuck up lol....arrrgggghhhh FORDS!!!!

Right peeps need help...

this is not a wess story BTW

Just today, was having a wee pop at my mates m3 csl, and i accidently hit the limiter in first gear,was too busy looking at me sitting a car length in front of him and laughin, as you do - Anyway, we had a bit of craic etc, but now everytime my car come on boost its backfiring like a MOFO...sounds like a boost hose has come loose but it hasnt, all are tight as fook and i dont have a clue whats wrong...
Its a T25 escort cosworth, which has, as of 2 days ago, an airfilter and stage 2 GGR chip put into it, ive checked the chip, its fine and ive checked the filter, what else could it be?

HELP!!!!!