Should I run both sensors if theres no cat in the aftermarket exhaust. It was a full cat delete exhaust with headers.

 

Ahh, so you're the one who caused all this global warming? Just kidding! I'd say you need the upstream 02 sensor since the computer uses it to adjust the air/fuel mixture. The downstream sensor will serve no purpose wtithout a cat, other than turning on your CEL. I've seen a gizmo sold on the net that you can install on the sensor to keep the light from coming on, but I have no idea if it really works or not.

 

Ok thanks alot. I just put a brand new upstream o2 sensor in and the light came back on for no signal from downstream o2. Also I have a cold air intake and heavy rain affects the way the car drives...any way to keep the water/moisture away?