do any of you people with de-cats/gutted cats use oxygen simulator sensors or just plug sensors back into the exhaust ??

 

You always need the upstream O2 sensors. If you have a OBDII car with both upstream & downstream sensors and you do away with the cats, the downstream sensors will complain that the cat is not working. You can use the O2 sims in place of the downstream sensors to send a fake signal to the PCM, or you can tune out the downstream sensor feature from the PCM.

 

thanks, thats what i was going to do with the downstream ones, however does this make the car run fine or is it better to tune it out??

 

Makes no difference on how the car runs, the idea is to keep the check engine lite off.