I have a 1988 ford mustang with new engine.I have had backfire problems since firing of motor.When i open it up it backfires and loads up.I have rechecked timing and made sure wires where not crossed.I have new tps,ibp vavle and just replaced egr valve.I set tps sensor and its okay.The motor does have the smog pump off of it and the back of heads plugged.There is new exogen sensors in exhaust.The motor starts fine but after a few minutes will load up with fuel until i clear it out.I can kill switch and restart and it will run fine for a few minutes and load up again.I have checked for vaccum leaks but haven't found anything.The egr valve helped the backfire problem.The engine also has an e303 cam in it.If anyone else has had this problem some advice would be appreicated.