MAP sensor voltage to kPa (B2101, B2102 and B2103)

[Gelf VXR]

Hi, many threads about scaling the MAP sensor voltage, can anyone show the formula that includes the data for the 3 calibration? Thanks in advance

B2101 - Used to scale the MAP sensor voltage output into a kPa/psi value.

1bar sensors are typically - 94.429688



B2102 = 2nd Offset value applied to the MAP sensor value.

Eg -
94.429688 / 3 = 31.476563 (where does divide by 3 come from, why is the result the value of B2102???)


B2103 - Offset value applied to the MAP sensor value.



Formula? but this doesn't work,

kPa = V*{B2102}+{B2103}

[Gelf VXR]

I found a calc.pid for a 3bar sensor

*CLC-00-042
kPa 0 300 .1 "{GM.MAP}*288/5+10"


For 1 bar sensor, it should read in my case taking the values from the PCM "{GM.MAP}*94.429688/3+10.332031"

So

0.1v = 0.1*94.429688/3+10.332031= 13.48kPa

1v = 1*94.429688/3+10.332031= 41.81kPakPa

4.5v = 4.5*94.429688/3+10.332031= 151.98kPa


What am I doing wrong?

5v = 5*94.429688/3+10.332031=176.8kPa

[joecar]

Hi GVXR,

Please post your tune file and the calc_pids.txt file that contains that pid.

[joecar]

Sounds like the formula should be something like this:
kPa = V*{B2101}+{B2103}

[joecar]

Sounds like the formula should be something like this:
kPa = V*{B2101}+{B2103}

Hmmm, that's not right either.

[statesman]

I found a calc.pid for a 3bar sensor

*CLC-00-042
kPa 0 300 .1 "{GM.MAP}*288/5+10"


For 1 bar sensor, it should read in my case taking the values from the PCM "{GM.MAP}*94.429688/3+10.332031"

So

0.1v = 0.1*94.429688/3+10.332031= 13.48kPa

1v = 1*94.429688/3+10.332031= 41.81kPakPa

4.5v = 4.5*94.429688/3+10.332031= 151.98kPa


What am I doing wrong?

5v = 5*94.429688/3+10.332031=176.8kPa

You're dividing by 3, that's what you're doing wrong. Try dividing by 5.

[Gelf VXR]

That calc.pid is yours I found in another thread. I'm thinking this should be really easy, only thing I can think of is first scalar is at one voltage and the second another, that's the calculation for the slope, and offset is the offset. But what are the relative voltages for the known scalar values?


Hers an example I've seen else where for a 3 bar sensor

DSteck wrote

It's the same as part 0 281 002 437... A 20-300kPa sensor that uses Characteristic Curve 1.

0.4v is 20kPa
4.65v is 300kPa

Work the mx+b and you'll find a MAP Sensor Linear of 329.41kPa and a MAP Sensor Offset of -6.35kPa.

That screen shot is showing the linear per volt. You need linear per five.

329.411764705882 and -6.35294117647061 if you really want to push the digits out.


P1 (20kPa) occurs at 0.4v and P2 (300kPa) at 4.65v. The slope is (300-20)/(4.65-0.4) which is 65.88. Multiply by five to get the linear value (which is how much range the sensor has over 5v). That's 329.41.

4.65v would be 306.35kPa of range (329.41*(4.65/5)). Subtract that from 300kPa at 4.65 and you get the -6.35kPa offset.

[Gelf VXR]

You're dividing by 3, that's what you're doing wrong. Try dividing by 5.

From EfiLive Calibration?


2nd Offset value applied to the MAP sensor value.
This value would typically be {B2101} "MAP Sensor Scaler" divided by 3.
Eg -
94.429688 / 3 = 31.476563
or
188.000 / 3 = 62.667

[Gelf VXR]

I think I solved it, maybe, without knowing the reference voltages for sure, but if I consider 4.5v for {B2101} and we know {B2103} the offset at zero volts, then


kPa = V*({B2101}/5)+{B2013}


{B2101} = 94.429688 and {B2013} = 10.332031


kPa = v*(94.429688/5)+10.332031

kPa = v*18.8859376+10.332031



0v 10.332031kPa
0.5v 19.7749998kPa
1v 29.2179686kPa
1.5v 38.6609374kPa
2v 48.1039062kPa
2.5v 57.546875kPa
3v 66.9898438kPa
3.5v 76.4328126kPa
4v 85.8757814kPa
4.5v 95.3187502kPa
5v 104.761719kPa

[joecar]

So this is it...?


kPa = V*({B2101}-{B2102}/3)+{B2103}

The coefficient for V is complicated...

[Gelf VXR]

I'm not convinced, I'm hoping some one will come along and confirm or advise the correct formula

[Gelf VXR]

Some general information here

https://splitsec.com/wp-content/uploads/technotes/TN6_Fuel_an_Engine_in_Boost_using_a_2_bar_Map_Sens or.pdf

A naturally aspirated engine uses the vacuum generated by the intake cycle to draw in the intake
charge. The manifold pressure depends on the throttle position. When the throttle is closed the
engine pulls a strong vacuum against the throttle resulting in a low manifold pressure. At idle
this pressure is around 1/3 of atmospheric pressure. Since the output voltage of the map sensor is
linear with pressure, with a nominal full scale output of 5 V, the output voltage at idle will be
approximately 5/3 = 1.67 V.
In practice, the full scale output of a map sensor is usually a bit less than 5 V. There is a
variation among sensor manufacturers and part numbers, but a typical full scale voltage is around
4.6 V. During normal operation the map sensor reading will vary between about 1.5 V and 4.5
V. High vacuum can be generated on deceleration resulting in output voltages less than 1 V

[joecar]

Most ctz files I looked at have only B2101 and B2103... I would like to see a file containing B2102.

[Gelf VXR]

Most ctz files I looked at have only B2101 and B2103... I would like to see a file containing B2102.

I was just about to say B2102 is a red herring

[Gelf VXR]

B2102 is in the tune file I posted earlier, snap shot attached.

I exported some log data for GM.MAP volts and SAE.MAP kPa, checked it in spread the formula is ok

[statesman]

You get a very similar outcome if you just use the simpler equation dividing by 5.

kPa = V*{B2101}/5+{B2103}

[Gelf VXR]

You get a very similar outcome if you just use the simpler equation dividing by 5.

kPa = V*{B2101}/5+{B2103}

The penny dropped, thanks :)