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By 5peedmanual
#61665
My map sensor reads :
0,9V at iddle
4,1V with ignition on and at max acceleration

How can I calibrate this at 0V? since its not atmospheric pressure, and I can I know how many kpa is at max acceleration? Can I calculate it with engine cc etc?
User avatar
By PSIG
#61669
First, I assume you have read the Wiki section on MAP calibration?
5peedmanual wrote: Sat Mar 04, 2023 4:38 pmHow can I calibrate this at 0V?
If your sensor is one of the numbers listed in TunerStudio pressure sensor calibration, it is already calculated for minimum and maximum pressure reference to voltage. If your part number is not listed, you can do two or more things:
  • Use the datasheets for your sensor and calculate the transfer function 0V and 5V pressures to enter into calibration as a custom calibration
  • Check similar sensors for the same transfer function values, and if it matches perfectly (sometimes), just use that provided calibration
Remember, the calibration uses the pressure at 0V and 5V, not the voltage at 0kPa and max reading. Most sensors cannot read to 0kPa. If testing accuracy, use the functional results, e.g., atmo kPa (current barometric pressure), against current conditions at your location. A more accurate test of your location will require more accurate test equipment, so you are not testing against junk (like a cell phone sensor).
5peedmanual wrote: Sat Mar 04, 2023 4:38 pmsince its not atmospheric pressure, and I can I know how many kpa is at max acceleration? Can I calculate it with engine cc etc?
The sensor reads atmospheric pressure at power-up, or at intervals if real-time baro option is used. TunerStudio calculates the engine displacement with other factors to produce an estimate for the VE Table, but due to other factors and errors, is not a true representation of volumetric efficiency of cylinder filling.

As barometric pressure (atmo) varies, and VE is relative based on many other factors such as air filter restrictions, exhaust efficiency or state of tune; it is difficult if not impossible to predict accurate kPa at max acceleration. Fortunately, the actual MAP kPa is reported and logged (if desired) for any conditions, including max acceleration. These actual results are then used as references in tuning. We want calibration, but do not want to "zero", as the values are relative to current actual.

I hope I understand your questions and helped to answer them. If not, please be more specific, or provide the purpose of the exercise. There are often different ways to approach info or solutions.
User avatar
By 5peedmanual
#61670
Thanks for the reply. I've managed to get this technical data from my sensor
Pressure range (bar): 0.17 - 1.17 BAR (17-117kpa)
Should I plug 17kpa at 0V and 117kpa at 5V?

My question was regarding what info I had about the sensor and how to use that to calibrate the sensor. Since I only had those voltage readings and no Info on the sensor kpa range I was wondering If I could use what I had.
I'm using a 0261230031 bosh sensor btw, thanks again
User avatar
By PSIG
#61676
It is more likely 0.17-1.17 is the total range, not the readings at 0 and 5V. If I was testing it, I would use a vacuum tester (hand pump), measuring the signal voltage at various pressures and extrapolate a linear slope (most of these are linear). Else perhaps use a similar calibration (MPX4115 or MPXH6115) or your numbers at 0 and 5V, to get initial response, then check for errors in order to adjust the 0V and 5V points. How to get an answer largely depends on what you use to compare readings or voltages. What is your comparator? ;)

Now, having said all that, if it will only be used on this vehicle it will work even if only "close" to being right. This is because tuning to sensor readings is not absolute, but relative. If the current MAP is reading 30 kPa, and reality is 35 kPa, it will run fine as it is tuned to run correctly at the indicated 30 kPa, no matter the actual pressure. The readings must be reliably repeatable for this to work well, so it must always read the same at the same pressure. I hope that makes sense, and why typical factory tolerances of 5% + or - are typically acceptable, and yet worse still runs fine if tuned to that error.
User avatar
By 5peedmanual
#61714
Gotcha, I dont see myselft getting and handpump so I guess I'll go and try to manage the error. I connected the obd scanner and got and Idea of the readings. At open trottle I get around 100 kpa and riding slow close to idle got to aroud 49kpa. I got confuse reading the VE table. The first cell is at max kpa, so in the first acceleration zone and I thinking it should be in the idle zone, so in the cells below with low kpa. But it should be in the ones above right?
Thanks for the help
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