Hey guys trying to figure out how to rescale the sensor correctly. I got a CTT 10 Bar Map sensor. 0.5v = 4.35psi and 4.8V = 145psi. The stock file at 0.499v is 19.948 and 4.501v = 174. Why is the stock sensor set up this way? Wouldnt the ECM start at 19psi at .5v then? I know the stock sensor is only a 3 Bar, so how does the scaling work if it is set from 19psi to 174psi from the factory?
Last edited by TwistedShafts; 03-02-2021 at 06:18 PM.
Huh? The stock map sensor isn?t set a max of 174psi. It?s scaling is 102 counts to 921 counts and 11.99 inHg to 104.74 inHg respectively. Or, 0.5v to about 4.5v and 5.89psi to 51.44psi.
This is an absolute pressure sensor, so it reads atmospheric and boost pressure combined so it needs a wide range and it?s a linear sensor.
I do know that it reads absolute and the stock sensor only goes up to 51psi. I don't understand how the voltage to Psi scaling is set up in Hp Tuners. It doesn't make sense to me. I will add a picture of what I am talking about in the above statement.boost.PNG
In the attached picture it shows app. 19psi at .49v and 174psi at 4.5v. That is how it shows up in Hp Tuners. That part doesn't make sense to me. New Map sensor scaling is as stated above " 0.5v=4.35psi and 4.8v= 145psi.
That scaling is wrong and the sensor only reads between 0.5v and 4.5v on the stock sensor and the 10 bar sensor only reads between 0.5v and 4.8v. Actually uses an ADC and it?s native format is counts, not volts. Anything outside those volt ranges the sensor just stops at the min or max value it can output.
The information out there for scaling the 10 bar map sensors isn?t quite accurate either. 10bar certainly isn?t 160 psi. It?s 145.04psi.
This is what I use and it follows a mechanical gauge very well.
Volts: 0, 0.5, 1.36, 2.22, 3.08, 3.94, 4.8, 5
Psi: 4.35, 4.35, 32.49, 60.63, 88.77, 116.91, 145.04, 145.04
Thank you so much Jim! I will give that a try tomorrow. The way Hp has it in there confused me so bad lol.
Don?t trust HP Tuners scaling on everything, they have errors in lots of spots for scaling.
Thanks Jim I was looking for this also!
i have a question if the scaling is wron (beacaue of errors) did this screw up the tune because if i upload a tune i also upoload the wrong scaling, or did i think wrong, because if i change the scaling becaue of a 10 bar sensor i also upload the new scaling into the ecm?Originally Posted by Jim P
thanks kevin
Specifically with 5.9 Cummins, I don?t know if it?s all 5.9 Cummins calibrations or some, the values in the HP Tuners software is not correct. If left alone and using the stock MAP sensor it will not affect anything. In the HP Tuners software it is nothing more than a representation of the hex values in the calibration. If the representation is wrong and you change it for a 10 bar map sensor, without accounting for the error in the representation, then what you change it to will be wrong in the calibration.
Here is what is in a 2005 5.9 Cummins calibration in it's native format:
Counts: 0, 17, 18, 101, 102, 921, 922, 1022, 1023
inHg: 11.99, 11.99, 11.99, 11.99, 11.99, 104.74, 104.74, 104.74, 104.74, 104.74, 104.74
What HP Tuners software shows in the MAP sensor scaling for pressure in inHg: 40.614, 40.614, 40.614, 40.614, 40.614, 354.703, 354.703, 354.703, 354.703, 354.703, 354.703
Way the f*** out to lunch on their conversion...
Last edited by Jim P; 04-04-2021 at 08:35 AM.
For the sensor voltage, it runs through an ADC to go from analog to digital. You get the voltage from the native "counts" with some math. For the MAP sensor ADC on the 5.9 Cummins it has a maximum of 1024 possible values, ranging from 0 to 1023. The sensor is supplied with 5 volts, with a readable range of 0.5v to 4.5v. 0 counts is obviously going to be 0v.
17 counts will be (rounded to 2 decimal places): (17/1023)*5v = 0.08v
18 counts will be: (18/1023)*5v = 0.09v
101 counts will be: (101/1023)*5v = 0.49v
102 counts will be: (102/1023)*5v = 0.50v
921 counts will be: (921/1023)*5v = 4.50v
922 counts will be: (922/1023)*5v = 4.51v
1022 counts will be (1022/1023)*5v = 5.00v
1023 counts will be: (1023/1023)*5v = 5.00v
Each count equals (rounded to 8 decimal places): (1/1023)*5v = 0.00488759v
So the range the MAP sensor will read is 0.5v-4.5v & 11.99inHg-104.74inHg. Or converted to psi, 0.5v-4.5v & 5.89psi-51.44psi. Keep in mind this is absolute pressure, so atmospheric pressure plus boost pressure.
The correct conversion factor for the pressure axis of the MAP sensor scaling is 0.0159064138077 and in inHg. The values are in 16bit unsigned format. In hexadecimal, the absolute max that can be entered is FFFF or FFFF in decimal format 65535*0.0159064138077 = 1042.427inHg/511.992psi.
Stock pressure values for the MAP sensor is 02F2, 02F2, 02F2, 02F2, 02F2, 19B9, 19B9, 19B9, 19B9, 19B9, 19B9. Convert these to decimal and they are 02F2=754 & 19B9=6585. With this and HP Tuners values of the pressure axis we can find out their conversion factor used. Either or, both will yield the same value, 40.614/754=0.0538652999240699 or 354.703/6586=0.0538652999240699.
A 10bar MAP sensor is 0.5v=4.35psi/8.857inHg & 4.8v=145psi/295.223inHg.
The conversion factors given are for inHg. If we change the MAP sensor axis values to that of a 10bar map sensor without accounting for the error in the software, what we would end up with for scaling is:
On the lowest value, bring to raw decimal format: 8.857/0.0538652999240699=164.4304, multiply by real conversion factor, 164.4304*0.0159064138077= 2.616inHg or 1.284psi
On the Highest value, bring to raw decimal format: 295.223/0.0538652999240699=5480.823, multiply by real conversion factor, 5480.823*0.0159064138077= 87.180inHg or 42.819psi
ok thanks for this great explaination
There are even PID?s in the VCM Scanner I have come across that clear as day have the incorrect conversion factors in the software.
Jim,
I tried scaling the 10Bar map sensor as you had stated above. With the key on and engine off it is reading 3.8psi. Before with the factory sensor, it read 13.5 for atmospheric. I can't seem to get it to read atmospheric with engine off with the 10Bar sensor.
Post your tune up. I set up one for 10 bar not long ago and it worked just fine.
2005 Dodge Ram 2500 5.9 Cummins 10Bar Map Sensor First Alteration.hpt
Hopefully, you can see what is off with it. I have tried a few different ways but not successful.
Last edited by TwistedShafts; 04-30-2021 at 09:59 PM.
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