If i install a catless downpipe i dont need to run the O2 sensors do I? also could i run run it without a tune for 2 weeks without any problems? thanks

 

The car fuels off of the primary lambda sensor, which is pre-cat, so it won't hurt the car from that standpoint, but you will have a CEL.

The O2s need to stay in place and your tuner needs to tune the DME for there not being a cat there, otherwise you'll have a CEL.