Rear O2 sensor reading all over the place

[Brian83]

Sorry, another new thread about my jeeps issues. 99 4.0 with Federal emissions. So one down stream cat. New NTK O2 sensor front and rear. Was reading a steady .89 and found the Cat had been gutted. Replaced the Cat/Head pipe with one from Rock Auto. Eastern Catalytic I believe. Now my rear O2 sensor is all over the place. Ranging from .15 to .75 and everything in between when it should come up to around .45 and stay steady at operating temp.. My first thought is the convertor, either defective or under sized. Talked to the local Jeep/Offroad shop owner and he said maybe I dont have enough restriction in my exhaust. Its a straight through Thrush muffler with a dump infront of the rear axle. Im looking for any input or ideas on what may be causing this rear O2 sensor issue.

Thanks guys,

 

[qslim]

My suspicion would be the catalyst as well. The only thing that flattens the wave of the secondary sensor is the catalyst performance - when the rear 02 sensor reads a wave like the front 02 sensor it means the catalyst isn't doing anything to change the content of the exhaust.