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ECUflash MAP sensor scaling for ECUFlash...ready to hurt your brain?

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H@xtGSX

10+ Year Contributor
1,093
9
Aug 9, 2011
Carlsbad, New_Mexico
I just spent 4 hours going through the scaling of the map sensors in ECUFlash to see if I could figure out how to add a custom one, and I discovered how it works. I am not a programmer, but I have done a little, so I understand some of the very basic concepts... Now I am going to try and explain in plain terms what I learned, so you all can tell me if I am wrong, because this could be useful for using cheaper Freescale MAP sensors for speed density set up.

Ok, first thing is Ceddy used 10 bit hex for the sensor resolution, which means that there is 1024 single bits to represent a figure. The figure used for the MAP sensor is the voltage, which is assumed 0-5v for the computer, although the sensor max output voltage may be slightly lower. Same applies to the minimum voltage.

Using the GM 3 Bar sensor already in Ceddymods as an example, it has a max voltage output of 4.89V. It is assumed the sensor reads up to 349.9KPa for safety. To see this, select SD MAP Calibration, click edit, pick edit map definition, and at the bottom of the next window hit the scalings button, then scroll down to MAP 10 bit (GM 3 BAR), click it and hit the edit button. That'll bring up the edit scaling window, where you can see all the values.

When the sensor output is read the raw voltage number is put into the 10 bit hex bytes as it reads. For example, if the sensor were outputting 2.46V, it would be 02 46 in the hex bytes. Convert that hex number to decimal and you get the 582 shown in that window. Now, if you know the KPa at a given voltage (such as the max voltage and assumed max KPa), you can divide the KPa by the decimal number you get from converting the hex byte number, which will give you the formula number needed for the ECU to calculate the MAP pressure.

Like this, using the GM 3 bar max values:

4.89V = 04 89 hex bytes = 1161 decimal

349.9KPa / 1161 = 0.3014

.....so for the ECU to recognize the pressure, it multiplies the decimal number derived from the hex bytes by 0.3014 and has the pressure in KPa to reference the speed density tables. That's how it goes from the raw voltage from the sensor to a number used in the speed density calculation. So, if you have the technical data sheet for a given sensor, you can extrapolate out the digital conversion formula for use with Ceddymods SD. Now, there is a bit more to it than this, but if you understood this, you can figure out how to get the sensor entered in very easily. Just use the "ADD" in the Scaling Manager screen (where the formula figures are shown) and enter it in like the other MAPs are shown.

I know that was a lot, but I hope it is useful info for someone. I spent a long time muddling through it with no prior understanding of it, but I read a lot, and did a lot of math, and it worked for my little 20-250 KPa sensor, which was $14 vs. $75 for a GM 3 bar. :D
 
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