Im having a similar issue with a GM 3-bar map sensor. with the KOEO evoscan shows +3.6PSI. for now im going to edit the formula in evoscan (and my tactrix logcfg file). Im pretty sure its not my scaling but this is what I have found.

Voltage - PSI
0.00 -14.2
1.00 -5.5
2.00 3.6
3.00 12.9
4.00 22.0
5.00 31.1