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Section 4.1: Manifold Absolute Pressure


Section 4.1.b: Wiring

The standard is for the MAP sensor to be placed on-board, but it can be located outside of the Genboard v3 case. In the case you would locate the MAP sensor outside of the case, some alternate wiring is required. This wiring can be requested when ordering your Genboard v3, or can be done by you by simply running an air-wire from the MAP Signal lead to an unused EC connector pin.

Section 4.1.c: Installation and Upgrade

Fitting the MAP sensor

Unlike most other engine management units the manifold pressure sensor is integrated onto the main circuit board. To fit the sensor onto the board the legs must be bent twice at 45 degrees:

Installation of MAP sensor

Note that the part number is facing up.

Using two threaded screws to position the sensor, place it onto the underside of the circuit board:

MAP sensor in place on board

Once aligned correctly, solder the sensor in place. If you use steel screws and nuts to secure the MAP sensor you must use an insulating washer to isolate the screws from the tracks of the circuit:

Insulating washers used to isolate the MAP sensor

There is very little configuration for the MAP sensor, even though it is arguably the most important sensor in the system. Most people use the Motorola MPX4250AP 250kPa pressure sensor.

This (nonzero value) also activates the precise MAP calculation. Most people don't bother to calibrate their MAP sensor more precisely because tuned VE values compensate for even significant errors, but getting air pressure data from a weather station or nearby airport is useful. It's good to have precise reading on the LCD. Genboard v3 supports 512 kPa MAP sensors out of the box (more than 4 bar boost vs. original 1.5bar for the MPX4250AP), but higher pressure sensors can also be connected with kpafac=ff settings: VE and req_fuel settings can easily compensate, but LCD reading will be proportionally lower. The 1995 year BMW racers used 4 bar boost, except they used 5 bar boost at the qualifying rounds: had they used GenBoard v3 with today's firmware, their LCD reading would have been affected.

Section 4.1.d: Configuration

MAP Sensor Config Variables
Variable Name Starting point value Units Description
kpafac 0x7F (127) 0x01=2kpa Max pressure sensor is designed for. eg. standard Motorola sensor is 254 kPa, therefore 254/2=127=0x7f
kpaoffs 0x52 (82) 0x01=2kpa MAP signal offset. -32..+32kpa
baro 0x64 (100) 0x01=2kpa Mean uncorrected barometric pressure. Used as a limp-home value if sensor fails. You could use any pressure you'd like here, eg. higher pressure for richer fuel mixture settings on sensor fault.
dbaro 0x0C (12) 0x01=2kpa Max allowed difference in barometric pressure. If barometric pressure is less than baro-dbaro or barometric pressure is greater than baro+dbaro, use config.baro as barometric pressure.

Section 4.1.f: Testing and Monitoring

The MAP sensor can be tested by comparing values displayed in MegaTune or MegaTunix to uncorrected barometer readings. It can be tested for functionality by simply sucking or blowing through the sensor; if you are using the standard Motorola 2.5 bar sensor, your values will not need to be calibrated.

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