The last time I had the MegaSquirt on the test-bench, I noticed that the MAP gauge was reading low; reading ~94kPa instead of ~101kPa. I checked the setup parameters of the MAP gauge properties and the TunerStudio settings under the ‘Tools/Calibrate MAP/Baro’ menu options. All was well. I then checked the +5V rail to the sensor… it was OK (+4.9V). Damn, sensor up the s@#t!
I ordered a MPX4115 sensor instead of the MPX4250 as fitted. The MPX4115 is better suited to my naturally aspirated engine that wont see much higher than 101kPa. The MPX4250 goes up to 250kPa and is suited to boosted engines. The MPX4115 will also allow for a finer granularity of measurement.
Fast forward to today and I fitted the new sensor. I had to change the settings in the ‘Tools/Calibrate MAP/Baro’ menu to reflect the change of MAP type. I also found a GM 1 Bar MAP sensor in my box of spares, so I added this as the second MAP sensor and will use it as a Barometer sensor.
Before connecting to the MS via Bluetooth, I changed the properties of all the MAP gauges to reflect the new Min/Max settings (10kPa & 115kPa). Brought the MS up and the MAP gauge now read 102.2kPa. I checked the latest reading for my area from the weather bureau and it was 102.98kPa normalised to sea level. I plugged this into a online air pressure to altitude calculator and entered my altitude of 26.7 meters. It gave a corrected value of 102.6kPa; so close to my reading of 102.2kPa… ~0.4% difference, well within the maximum 1.5% FS error range of the sensor.