any idea what 'byte' is giving me my A/C pressure, $DA2

dizwiz24 · Post by **dizwiz24** » Wed Jun 30, 2010 5:28 pm

My A/C pressure output is an analog 0-5 volt output, that shows up as a pressure when a datascan is made on my 93 lt1 corvette.

Id like to know what equation (what conversion factor) the $DA2 program is applying to translate that volts to pressure. Id like to be able to back calculate the volts from pressure.

Can anyone help me out, or point me where to look in the code?

I dont really know how to look at the code....

on some of the later model lt1 cars (94-95) its 'byte 30'.

Post by **robertisaar** » Wed Jun 30, 2010 8:17 pm

i'd have to look at the source files, but who's ADS or ADX for DA2 are you using?

dizwiz24 · Post by **dizwiz24** » Sat Jul 03, 2010 9:43 am

robertisaar,

It says DA2.ads
version 1.1 92-93 LT1

I use the tunerpro data logging software to look at datalogs...

Sometimes I also use TTS Datamaster to look at the datalogs..

Post by **robertisaar** » Sat Jul 03, 2010 10:07 am

in both my DA2 ADS and the source file, byte 20 is the A/C pressure reading. the equation is PSI = (N * 1.875) - 18.75.

i'm not sure why you would want a voltage reading honestly, PSI is much more useful.

dizwiz24 · Post by **dizwiz24** » Sat Jul 03, 2010 2:49 pm

im assuming N is volts...

what im doing with the A/C pressure sensor is as follows:

I removed my A/C (hence no need for A/C pressure sensor) and hooked up the 0 to 5 volt output of my AEM UEGO wideband O2 sensor into the place of the A/C pressure sender (which is also 0 to 5 volt output).

This way when I do scans, I now have wideband o2 sensor info (after I use that equation you gave me to convert PSI to volts) right alongside RPM, MAP, and the other operating parameters.

You really helped me out. thanks!

Post by **robertisaar** » Sat Jul 03, 2010 2:53 pm

i see... for my applications, i like the low coolant level sensor, since it won't disrupt anything tuning wise... but since you have the a/c gone, as long as you don't try and use it, i don't see any problems happening.

dizwiz24 · Post by **dizwiz24** » Tue Jul 06, 2010 9:30 am

I just pulled tried this and it works. I can backcalculate a voltage based on the equation you gave me and knowing that volts = 5N/255

I can then look in a table, supplied with my wideband sensor, to see what AFR that voltage corresponds to.

robertisaar,

I didnt think any fueling/ ECM changes results as a change in A/C pressure? Or am I mistaken? you say dont try and use it. do you mean that something odd will happen if I do? the compressor/ condensor and stuff is all removed.

I thought A/C pressure is monitored solely for scanning purposes (ie. not an active input to ECM).

Post by **robertisaar** » Tue Jul 06, 2010 9:36 am

in certain masks, the ECM/PCM uses the A/C pressure to determine how many steps to open the IAC when it's turned on, raises idle speed by so much, a/c on fan enable pressures/temps, etc...

and that's just the $DF mask, which was only used from 91-93 on LQ1 cars and 93-94 LH0 W-bodies...

other, more comprehensive, masks, likely use it for even more...

but, as long as you never accidentally try and turn on the A/C, it will likely not do anything, depending on how the algorithm is setup.

dfddfd2 · Post by **dfddfd2** » Tue Jul 06, 2010 3:30 pm

The AEM UEGO uses (V*2)+10=AFR, so in your case AFR=(10N/255)+10.