sputtering and back fireing

my 95 XJ is sputtering and back firing like a shotgun out from the undercariage. it was doing the same thing a month ago when i had a cracked exhaust manifold so i swaped it out it stoped until now it has started again. and the check engine light is now on. what could it be?

get the codes from the computer and you'll get a good lead on it. the local parts store around here will read codes for free.