O2 sensor location?

O2 sensor in right location?

On my '99 what is the proper location in relation to the catalytic converter for the downstream O2 sensor (second O2 sensor)? The previous owner had the exhaust modified and the downstream O2 sensor is before the cat. Isn't it supposed to be after the cat? For my own knowledge, does it matter were the sensor is in relation to the cat? Should I weld in another bung after the cat and move the sensor? Thanks in advance for the help!

No one knows??

from my limited knowledge and what i have read on here i don't believe it matters as long as it is downstream somewhere. i would save the effort and leave it where it is now. i know on my 00 it is after the cat to answer your first question.

upstream = before cat (responsible for determing optimum fuel/air ratio)
downstream = after cat (measures efficiency of catalytic converter)

Are you seeing a check engine light? Mods like this can really mess with the OEM design and oftentimes trigger the CEL.