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Old 12-09-2012, 07:22 PM   #8
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Member#: 284792
Join Date: Jun 2011
Chapter/Region: RMIC
Location: Vanilla Valley, CO
2011 STI


Originally Posted by dsm_luck View Post
If I got a wideband and the rear 02 is going out then wouldn't this still effect my tune? I know that on the newer WRXs the rear effects closed loop. Also i am curious as to why you cant use the stock sensor to monitor is you are catless. I understand its not as accurate as a wideband but shouldn't it do the job for just monitoring?
Your rear o2 is there to monitor the cats efficiency. It won't really affect your tune, except you will get a CEL showing a rear o2 error that needs to be tuned out. The FRONT o2 sensor located in the up-pipe is what is actually reading AFRs for the cars ECU.

Originally Posted by dsm_luck View Post
I guess what I am getting at is that if I get a wideband and still have to replace the stock 02 that may be too much investment right now and I may just replace the stock 02.
Don't replace anything. Just ADD a wideband for monitoring purposes.

Originally Posted by dsm_luck View Post
Also I have been told it would be possible to hit 18 A/F under boost on E85 and not knock. So it may not be the 02 after all. Uhg been chasing this problem and throwing money at it for over a month now. I do need to get it hooked up to a wideband though to see what is really going on. I just wish there was a way to get a wideband without having to replace the stock 02 if its bad as well. I thought I read somewhere that you can trick the wideband into working with the stock voltage but I have no idea how that works.
Again, your o2 sensor is probably fine. Don't replace anything. The wideband gets its voltage from the car, but not the readings. The readings are 'real time' and can be logged with a piggyback ECU, but not the stock ECU (afaik).
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