Have a cracked muffler going to weld in a new one and remove the CAT ( no emissions where I live and its a 91 so its not doing much anyway) what size is the exhaust pipe going into the CAT? looks to be 1-1/2 just want to be sure. Thanks.

 

You need to read this link. https://www.cherokeeforum.com/f2/cat...er-laws-24337/
Do you know that it is not a state law against removing it is a Federal law. It is not a topic that is promoted on this forum since it is illegal to remove any emissions component.

 

I was considering the same thing but on my 97 there are O2 sensors and it will throw a code if cat is removed. I wish there was a way to trick the bugger. My cat is shot so I tried putting the O2 from behind the cat out in fresh air and it just causes a real rich condition. No code though.

 

Did not know it was federal thanks for the heads up. What is the size comming out then so I can get the right muffler size?

 

You could always replace it with a "High Flow" cat. It'll flow better, and get ya a different, better sound that way your still legal. Gotta watch the o2 sensor codes though, some high flow cats will trip them. I had a high flow on my old saturn and it would trip randomly, sometimes it'd go months, sometimes it'd go weeks.

 

The rear O2 sensor does nothing with regard to controlling A/F ratio. The front O2 sensor does not sense anything regarding cat condition.

 

The rear sensor does have some control with gas mileage and a/f ratios... This has been covered ... In other threads

 

All I can say for certain is when I took the O2 sensor out and let it sniff fresh air my mileage went from over 21 to 17.

 

Lots of variables cause mpg to go up/down.....rear O2 is not one of them, purely coincidental.

 

the rear sensor is just for a CEL isn't it?

 

pretty much:turned :

 

Lots of things get covered in other threads.....some good info and some bad info....problem is, the bad info bell can't be un-rung and just keeps getting perpetuated in forums and on the Net.

From the Factory Service Manual:

Upstream O2 controls A/F ratio
Downstream O2 detects cat deterioration (and sets a CEL).

 

Rear 02 is used to 'verify' the cat is there. There are ways to tune or fool the PCM into thinking this is still there.
Front 02's are used to fine tune afr. These are in front of the front cats, and sometimes put into the front cats. You need these.

The rear cat is generally used as a 'fail safe' and generally not needed. You can run w/o cats and not have issues, however as outlined above, cats are part of your emissions systems.

 

To the op I think stock piping is 2.25

 

Look around http://performance-curve.com/index.aspx hes a vendor on here has nice cheaper exhaust kits and cats.