muffler issues

Has anyone had a problem putting mufflers on 91 rodeos. I put one on that is not a proper replacement and am having problems. The check engone light came on as soon as they put the muff on. I looked at the muff and it looks backwards acording to the arrows on the muffler itself. Iwas wondering if you could have a muffler the wrong way. Anyone with similar experiance please help

Hey there
If the arrows on the muffler facing front of the vehicle it means a 100% backword ,who is that briliant guy that put it like this:shakehead

A place in red deer. I went there today and they started giving me atitude and wanted to charge me to check out the vehicle. I told them where to go and said i'll go to a real shop and ill be back with the bill

what dumb asses...it even shows on the muffler the way the flow is suppose to go....