I have and old Greddy map sensor that came with the e-manage blue, I am starting the switch to sd and would like to use this sensor to keep costs down. I have the sensor logging correctly using an equation I found ((0.18375*x-14.333)*1.47. My question is about xml formulas I came up with

<scaling name="kpa Greddy" units="kpa" toexpr=".441175*x" frexpr="x/.441175" format="%.1f" min="0" max="400" inc="0.1" storagetype="uint16" endian="big"/>


I am new at this just wondering if someone could check this out and let me know if it will work. Thanks in advance.

 

Could you please explain how did you work out that expression for ecuflash scaling?

I want to use Defi map sensor for direct boost control, and SD. For now I could only find equation for evoscan for loging absolute pressure in psi, it is "0.216208*x-6.011667" (divide by 14,5 for bar).

I am also wondering how to find expression for "Boost error" in "Boost error correction (PSI)" table for direct boost control.

Defi map sensor shows 1,86v @ 1bar (0 boost) and 4,49v @ 3 bar (2bar boost)

 

as I understand "kpa Greddy" would be x*0,490467-50,082759

and evoscan formula would be 72,54/255x-21,762 for psi (divide by 14.5 for bar)

 

Could you show how you get the kpa scaling. I got close to the same thing for evoscan but the kpa scaling is confusing me. When I put that kpa scaling in ecuflash it doesnt look right, I thought all of the values needed to be positive, or do you just set them the same like you would normally do.

 

Set them the same like you would normaly do. Notice the negative numbers when switching between scalings for different MAP-sensors.

Evoscan formula is 72,54/255x-21,762 for logging psig. You can use -(21,762-14,5) adder instead of -21,762 to log absolute pressure.

72,54/(255+255)x - (21,762-14,5)/2 As I understand "(255+255)" and "2" dividers are needed because boost is using 2 bytes - boost adder+boost table (psi), 255 is map sensor 5v. And boost control is referring to absolute pressure, so we are using -(21,762-14,5) adder.

so 0,142235*x - 3.631 is the formula for direct boost control in psia8 and psia16 in ecuflash.

72,54/1023*x-(21,762-14,5) = 0.07090909*x-7.262 (psi)

0,490467 multiplier is for psi scaling and in kPa is (0,490467/14.5)*100=0.489028
7.262 is for psi scaling too and in kPA is 7.2652/14.5*100=50,082759

so the kPa Greddy will be 0.489028*x-50.082759

I'd be honest that I could not understand a couple of numbers at first, and it was partly a guesswork using analogy and comparing to the AEM 3,5bar known formulas calculations and numbers. But that is how I understand these expressions for now.

I also did the same calculations for my Defi MAP-sensor and now succesfully using direct boost control. That makes me pretty confident in my math. But I have not tested my calculation for SD. https://www.evolutionm.net/forums/8655096-post950.html

PS Waiting for gurus to join our discussion.

 

Thanks the negative values were throwing me off.

 

OK I figured out a small mistake in my math..

72,54/255x-21,762 is evoscan formula, it is correct. but..

For "kPa Greddy" it will be:

((72,54/1023)/14,5)*100x-((21,762-14,5)/14,5)*100 = 0.489028*x-50.082759

so correct formulas for kPa Greddy are:

to display: 0.489028*x-50.082759
and to rom: (x+50.082759 )/0.489028

PS corrected post #5 and PM-ed benpgreen

 

Thanks, as soon as I can come up with a GM IAT I will give it a try.