3050 pip engage difference front to back

I will try to explain this as best i can. The cam follower for pip engage on the front side was loose, hanging down about a sixteenth. I tightened it up, and did the 1st pressure calibration a few times. I now cannot get any image on the front side of the sheet. It seems the stepper motor is not rotating enough to bring the pip into contact with the blanket. Looking at the back side cam follower, it is a bit further around than the front.
What i have done :
Format raid array
Disassembled front pip engage assy. it is ok
Tried adjusting the BIDs, this changes the image, but does not fix it
Heres the kicker...
when i do the 1st pressure caibration, the press prints as i would expect, and i enter the values represented by the sheets.
Next i print the Grey20 file imported from CD, and i only get image on the press backside, about a quarter of the sheet.
My question: what tells the stepper motor for pip engage when to stop ?
I assume it is a command established by the software, run through the control board, since there is no other sensor.
Confused ? me too.
Any Thoughts ?
Thanks...