Just put my car (C5Z) back together following a clutch change. Getting lean WBO2 (Innovate LC1) readings now, around 16.5 AFR while both narrowbands are oscillating normally suggesting I should be around stoich. STFTs are averaging around +3, about even for both banks. While I had the exhaust off I had a bung welded in pre-cat as I was previously scanning post-cat (did the tuning with the wideband at the narrowband location). Obviously first thought was an exhaust leak, but I've retightened all the bolts and it seems there's no change. I have the WBO2 on the driver side part of the X-pipe, right before the cats and right after the DS header collector connects to the. No change after repeating the free air calibration. My question is, has anyone ever had a damaged sensor that wasn't reading accurately but also wasn't throwing an error code? Or is it possible there's a pinhole leak where the bung was welded? I inspected the weld after having it done with a light and couldn't find anything.
Exhaust system is Kooks. Here's a picture of what they look like with an arrow where the O2 bung is.
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