I recently pulled out my 2003 mustang gt for the summer. Since i pulled it out it has been missing and backfiring when under load. If i idle around town you can hear the miss still. but still idles half decent. Engine was just rebuilt begining of summer last year. Intake and throttle body has been upgraded from stock. Riechart Racing is what is written on the intake. Has a cold air and BBK headers along with full x-pipe and Bossani mufflers. Does have Snow performance methanol injection but is now completely disconnected. Was bored out .060. I am lost when it comes to newer cars with fuel injection. There are what i am told ignition coils directly on each plug. is it possible that one of them is gone? Is it possible that it's something simple like it needs a set of spark plugs? Let me know if you have n e idea.