Ok i need some help figuring this one out. I am trying to put on a custom exaust system and eliminate the cat. It looks like there is an O2 sensor in the front of the cat and then another one after the cat. From what I've heard, the computer compares the readings from before the cat and after to adjust the way the motor runs. I want to eliminate the cat without giving up my gas mileage. Its a 99 dodge ram sport 4x4 with the 5.9. Any tips would be very helpful.

 

you will need an O2 sim for the rear, otherwise you'll have a CE light. Also, having a 4x4 you may want to re-consider removing the cat because of possible low end torque loss. I have 3 on mine 2 are shells but the last is functioning and from what a friend (chevy 4x4) tells me on his truck, just changing to 3" between the cat and flowmaster caused a loss in low end torque and worse gas milage...

 

All right, I had problems with my cat breaking up so I had mine cut off. The 02 simm wasn't right and wouldn't fit where the sensor was so I have been running mine without the cat for about 2 months now. I have noticed the drop in low end torque, but I'm now getting a consistent 15 mpg and occasional 16's (city driving, 5.9L) That has been my experience so far with mine and I don't notice the check engine light anymore. If you want it to sound super good take it off. My two cents.
Ross

 

So how big of a loss of low end torque are we talkin here? And also, i think i was incorrect because ive been reading around about the o2 sensor after the cat and I think the only thing it does is tell the if the cat is working properly.

 

I think you are right about the second O2 sensor. If you get the O2 sim. then it just fools the computer in thinking that you still have a cat.
I have heard the same thing about losing low-end torque. I considered removing my cat. but did not want to lose low-end torque. Not sure what you want to gain out of this but it will make you exhaust louder. Check on e-bay at the muffler shop. They have a high flow cat for around $85.

 

I don;t know about removing the cat, but I have just recently replaced the 2nd o2 scensor with the thing that tricks the computer. I have not had a problem with that at all. IRight now I am running a flowmaster muffler right after the cat and noe exhaust pipe.

 

I hollowed out my cat. I observed no low end torque loss. I used an O2 sim from Caspers Electronics(on line). The price is 55$, excellent product.