i do this: Do not use custom map for that
Use Ecutek COOLANT PRESSURE (CP) sensor
you can scale your sensor there and apply SMOOTHING
put a smoothing of 0.2 (1 is no smoothing) and you ll have your output value much more stable and then with custom map you will refer to COOLANT PRESSURE to build a failsafe if you want
if you need help i can do it for you, otherwise ask your tuner to use the CP
same signal of oil pressure from rear 02, one with smoothing one without
edit: sorry didn t read well. you should NOT power your sensor with rear o2, you need a stable 12v possibly on key, change it ASAP