Oxygen sensor question

[Guest Tayousei]

Hi I searched and cannot find an answer to this question. The previous owner of my USDM tt supra had a shop make a custom 3" exhaust pipe straight from the first cat back. So where the 2nd cat normally is, there is what I believe is an O2 sensor (correct me if I'm wrong). Now it's just tied up with a zip tie and not hooked up to the exhaust. I'm ordering a downpipe anyway that has a spot for the O2 sensor and I'll probably buy a new sensor as well, but will I definitely see a difference hooking it back up? Eg. will it run better, more power or fuel economy, etc... Seems to me like it would. Or I guess more specifically, does NOT having it hooked up cause any specific issues?

 

I do notice compared to my friend's JDM stock Supra I seem to have a flat spot between 2k and 4k RPM when it's hot out. I was thinking it could need a colder grade spark plug due to increased boost (I get about 12psi max), or maybe IASC VSV... Fuel filter has been replaced, so its not that... Downpipe should arrive this week or next so I'll have a definitive answer soon enough, but would like to hear thoughts on the issue.

[SteveR]

I'm not 100% sure but that sounds more like a catalytic convertor (heat?) sensor.

[Jellybean]

99% sure thats a CAT heat sensor,as far as I am aware your car would run like crap without the O2 sensor (air-to-fuel ratio, enabling fuel injection to work efficiently)

[Chris Wilson]

It's the second reference O2 sensor used on UK and US market cars, and needs to be in the gas stream. Weld a fitting on the second de cat pipe and refit it.

[Guest Tayousei]

Well it's been off for as long as I've had the car and the downpipe I'm getting has the proper fitting already so I'll have it hooked up again soon. Any idea what having it disconnected does? (Eg too rich, too lean, ecu compensation based on 1st o2 sensor, etc)