What's the point in replacing rear (downstream) o2 sensors?

[poindexternasty]

hey all,

as the title asks, what is the point or purpose in replacing the downstream oxygen sensors on a stock 02 GT w/ 101k miles? I replaced my *up*stream sensors a few days ago to fix a low-rpm stumble, miss, and hesitation. The car runs great now but I am wondering if I should have replaced the downstream ones as well.

It is my understanding that the downstream sensors measure catalytic efficiency. If my cats are working properly (not smelling sulfur or gasoline in exhaust), should I still swap them out? Do they serve a real purpose that relates to performance, efficiency, environmental issues?

 

[SaleenGT2001]

their entire purpose is to make sure your cats are working. most people just eliminate them with a tuner.

 

[AdRock]

If you don't hacve a CEL telling you that their is a problem with them then don't worry about it it.

 

[Rusty67]

If you don't hacve a CEL telling you that their is a problem with them then don't worry about it it.

If you do throw a CEL/MIL I wouldn't replace them. An MIL eliminator is cheaper then a new O2 sensor.