This reference preserves the MAP conversion formulas and P72/P75 calibration values documented by the original pgmfi community. Use them to understand the archived ROM code, not as a universal calibration for every Honda ECU or MAP sensor.

Note

The source describes these raw values as being for P72/P75 code and says most OBD1 ECUs follow the same rule. Verify the actual ROM code, fuel-cut offset, and sensor calibration before applying the formulas elsewhere.

Basic MAP-byte formulas#

The archived notes assume that the stock MAP sensor's maximum reading is 1764 mbar.

Stock code halves the MAP byte:

pressure_mbar = (1764 / 255) * (map_byte / 2)

When the ROM's MAP value is uncorked, the final division by two is removed:

pressure_mbar = (1764 / 255) * map_byte

The same notes document these voltage formulas:

stock map: volts = (5 / 255) * ((raw / 2) + fuel_cut)
boost map: volts = (5 / 255) * (raw + fuel_cut)

The listed stock fuel-cut value is 24, editable at address 0x4DCC in the referenced code.

Voltage conversion notes#

The archived page includes these two linear conversions:

inHg = 20 * volts / 1.85 - 30.81
mbar = 365.9 * volts - 29.9

They are derived on the page from the following points:

Archived P72/P75 calibration values#

The following values are transcribed from the source. The first table uses the source's full raw-value labels, while the second shows the corresponding halved stock-map labels.

Caution

The source labels the final full-scale row as 256, although an unsigned 8-bit value tops out at 255. The value is preserved here as an endpoint label from the original notes.

Sensor interface#

Archived schematic for the three-wire MAP sensor interface.

Related#

• MAP sensor overview
• Understanding fuel and ignition maps