This plot shows the relationship between the output voltage and the vacuum that is applied to the MAP sensor.  This measurement was taken with a service grade vacuum gauge so there is probably some error here but it gets us into the ball park.  Also comparing known MAP values in the code to what I calculated here they were very close so this graph should be fairly close.  Below is a table taken from the code showing the relationship of Vacuum to Voltage to ADC value (L002a RAM location) and controller displayed Vacuum.
 

;
; The below table is what I measured for the MAP sensor that is in the '34
;  (11/14/98)
; The displayed VAC was obtained from the simulator............12/29/98
;
;   TAIR: 59 degrees
;
;   Vacuum    Voltage    ADC     L0000      VAC
;    (in)              (L002a)            TAIR=59
;      0        4.55     237      240      -3.2"
;      1        4.44     231      234      -2.4"
;      2        4.32     225      228      -4.7"
;      3        4.15     216      219      -0.6"
;      4        4.00     208      211       0.2"
;      5        3.82     199      202       1.4"
;      6        3.65     190      192       2.5"
;      7        3.463    180      182       3.7"
;      8        3.302    172      174       4.7"
;      9        3.141    163      165       5.6"
;      10       2.953    154      156       6.8"
;      11       2.809    146      148       7.8"
;      12       2.632    137      139       8.8"
;      13       2.415    126      127      10.2"
;      14       2.263    118      119      11.0"
;      15       2.136    111      112      11.9"
;      16       1.954    102      103      13.0"
;      17       1.783     93       94      14.0"
;      18       1.607     84       85      15.2"
;      19       1.437     75       76      16.1"
;      20       1.238     64       65      17.4"
;      21       1.061     55       55      18.6"
;      22        .874     45       45      19.9"
;      23        .695     36       36      20.9"
;      24        .510     27       27      22.0"
;      25        .316     16       16      23.2"
;      26        .134      7        7      24.3"
;      27        .024      1        1      25.0"
;      28        .024      1        1      25.0"
;      29        .024      1        1      25.0"
;