So the PO of my '94 cherokee thought it would be a good idea to cut out the cat and downstream 02 sensor. Wouldn't be that big of a problem, because we don't have smog here. But he didn't bother to put the 02 back in the new pipe. Without a cat, would it make a difference in MPG's or running rich if I tap a new downstream 02 into the pipe?

 

You should probably put a high flow cat in...

 

Go to performance curve and get a high flow cat with an o2 bung