This may help as well....talks about degradation as well http://wbo2.com/lsu/LsuInstal.pdf

FYI, I just moved my wideband sensor past the turbo. It was located before the turbo before. Just got through logging some runs, and it didn't make any difference at all with my readings.

Interesting... Makes me question the value of moving it...

Scott,
Did you mount before or after muffler?
Thanks

I have no muffler, but it was about 4" past the turbo.

I do not know if this information will be useful for you but in the assembly(editing) of my probe afr PLX advised(recommended) to install(settle) him(it) in approximately 30 "of the turbo, for me just after the silencer.

Thank you, Speedy Squirrel!

There are ways to read pre-turbo but it takes some plumbing. You have to take a small flow from pre-turbo thru like a 1/4 line and rout it into a small canister like a section of 1" pipe that has the wide band mounted in it. The discharge of the canister is large, like 3/4 tube and goes into the down pipe from the turbo upstream of the muffler or just dump to atmosphere on a race car. This way the WB sees the flow from pre-turbo but not the back pressure pre-turbo because the discharge from the canister is so much larger than the inlet from pre-turbo so you don't have to compensate the WB reading for the back pressure. This works for V's (or flat 6's) running a single turbo with ITB's and you want to trim AFR for each bank by having a WB on each side. Downside for a street car besides all the plumbing is carbon plugging in the small tube and you are constantly bypassing some gas around the turbo, not a problem on a race engine where it runs hot and is on the wastegate most of the time.