CHERO-NEWBIE

Hi Guys, my 96 cherokee sport 4.0 has no catalytic converter. (and is heavy on juice)I was trying to find the oxygen sensors but it seems there is no O2 sensor on my jeep, and that it might be in "open Mode"? (reply on previous post). Does this mean the ECU has default running settings no matter what you do to it? Would that explain why my MAP sensor receives 5.0v, but only gives out 1.8v on idle, no matter what I do to the O2 to input? I thought that at 4.0volt your jeep would be running lean, so if mine is running at 1.8volts, how come no damage has been done? is there another setting/apparatus somewhere that is riching out the mixture, irrespective of what the MAP sensor is saying?