Computer corrects too lean...

I have been tuning on a WB dyno recently and found my AFR to be in the high 15's at idle and part throttle when in closed loop. If I richen it up either by changing injector size or say adding 10% to the MAF table the computer starts throwing rich codes.
While tuning last night I took out my OBDII PCM so I had to throw in my OBDI PCM which was stock still - no programming. I have 30lb SVO's so this should have immediately went way fat but as soon as it went closed loop it went right back to the AFR that the OBDII PCM was at.

I have a scan showing TPS, MAP, O2's, RPM etc. from the obd-2.com's scanner. Anybody care to take a look?

I would just change out the O2's but they're only 3 months old. While scanning they move from .05 to .800 while idling part throttle etc.

Mods that could affect this:
long tube headers - cat delete with O2's removed and LT1 Edit disabled for codes
58MM NOS (Holley) TB
1.6 RR's
CMotorsports valve springs
RAISS (my intake - www.impalaperformance.com)
30LB SVO's - 31.71 lb hr and Millard's offset tables
Fbody MAF with associated tables from Herter
Nitrous (though not at idle or part throttle... :) )
TR6 plugs
Taylor Wires
New Optispark
New coil
New IAC
New Autozone MAP (quality???)


Hope you guys can help!
Mike

I'll reply to this myself, don't use a WB O2 in the tailpipe. It was reading high 15's at idle and low 15's part throttle. Put in an O2 bung into the header collector and wallah - perfect 14.7 through out the rev range. It only took 4 WOT calibration changes to get that to maintain a 12.7 through out. Picked up .3 in the 1/4 mile after getting done tuning.
:)
Mike