Turbo SD Closed Loop Operation Issues any ideas??

I just tuned a customer car with an ON3 turbo kit that I swapped a Comp 76 ball bearing to. Its a front mount kit on a 2000 LS1B car, stock motor, looks like flipped around truck manifolds. Anyway, I've got it dialed in nicely in open loop, idles at 14.5 AFR with the 60lb injectors (I did the transient pulse .cax mod), made 550rwhp at 9.5lbs, runs great. Soon as I put it back in closed loop it gets all messed up, starts running lean and misfires, force it back in OL and its perfect. The O2's are pre turbo in the bottom of the manifolds, has anyone seen issues like this due to backpressure/reversion, or what not? I messed with the switching point on the O2's (525mv) and it helped but its still not right. I suppose I can just leave it in OL but I'd like to have it run right in CL. Any ideas?

Thanks!!
Mike

Post log and tune files.

Are you running a COS3/5 or 1 Bar OS with SDCL? I always use a COS3 OR COS5 in semi-closed loop operation without an issue as long as the #'s match to enable the closed loop fueling. I've had issues running MAF's because of the built in IAT that would cause all kinds of fueling issues. But since your an F-body that shouldn't be an issue.

Is this a single turbo setup? If so, you can pretty well forget about getting closed loop to play nice.