U can run 14-15 psi no problem on the stock map sensor...u could even run a little more...short term fuel trims would take care of it to a point...I think the stock tune would limit the max amount of fuel added by the O2 by 25 percent
Basically the computer won't know how much to fuel to add or why but based on the lambda readings from the 02 it will keep adding fuel to the max allowed until it gets back to desired lambda...if the Desired lambda at wot in the last load column is set to .80 then it will aim for that when the load reaches max as defined by the tables