I just put a set of pacesetters on my 2000 chevy and I plan on running my current true duals without the cats. I still have my rear O2s hooked up and I am wondering if it will hurt anything to run them for a while with no cats until I can have them tuned out? Will it just throw a code or will it try and lean the engine out? Any help is greatly appreciated.

 

The rear O2's have no effect on fueling if I understand correctly, they only report Catalytic efficiency.

 

That is correct .

If the MIL is illuminated, engine performance should be affected though, as the PCM switches to pre-determined settings as a fail safe measure. But nothing will be harmed, as far as engine mechanical or sensors go.

 

Thanks a lot guys.