Hello, I am asking this question because my 1993 pontiac sunbird 3.1FI car was running great until my son-n-law took it to North Carolina and the muffler and converter fell off. His mechanic and hisself put on a straight pipe instead of replacing the catalytic converter, now the car runs rough and stalls sometimes when you come to a stop. What could be the problem, if not replacing the converter is not it?
Without the converter and the muffler there is no back pressure on the engine and you will eventually burn out the cylinders. You should replace the converter and the muffler in order to get the engine to run properly again.