Whats wrong with my 1999 olds alero
 

I have a 1999 oldsmobile alero it has the 4 cylinder. 2.4 I think. I replaced the starter now it cranks. I cut the cat off cause it was welded and needed replacing. However I havent put a cat on it. would the cat off would it.cau??se it to pop while acceleraring or just sitting cracked?? Or cause smoke ans barely make it up a hill and cut off??