NoPistons -Mazda Rx7 & Rx8 Rotary Forum - Safc Tied Into Fc Pressure Sensor Not Working....

Sorry for triple post here, i posted at teamfc3s.org as well... and rx7club.com

Problem/Question Time.

After 8 long months of what i thought was a group buy that went south big time, my safc finally came.

Installed everything. Everything works.

WOHOOO! score one for me.

I however splied the TPS wire into the stock pressure sensor.

Reference: (http://www.rx7club.com/forum/showth...=safc+AND+boost) it's down so i can't find my thread from a year ago.

What i know is this.

Stock pressure sensor output:

0V = -15 psi

5V = +15 psi

This can be confirmed by info from DIY FCD where paul stokes figured out the transfer function (equation of line) of the relationship between pressure and voltage output (http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm)

so we know this:

Out(V) = 0.169V/psi*P(psi) + 2.318V

Solving for Pressure, we get:

P(psi) = (Out(V) - 2.318V)/0.169V/psi

therefore for stock S5 TII which has max boost of 8.2 psig

this corresponds to 3.7038 Volts

The safc Throttle %, i'm assuming is between 0% and 100%, where 0% = 0V and 100% = 5V

therefore 3.7038V / 5V = 74.076%

So at 74.076% i should be at max boost.

But when i drive my car around, and boost her in 2nd up to 0.33 kg/cm^2 = 4.7 psig

the safc throttle % says i'm at 100% already. WTF?

4.7 psig should be 3.11 Volts or 62% throttle.

I'm dumb founded now.

When the car in the ON position it reads 65% throttle or 2.23 Volts

Fine! but 2.23 volts 5 = 44 %.

So i'm always off by 20% across the percentage range. So what i did was figure that 3.7/5 = 74% + 20%

but it is not working.

DALE! how the hell did you manage to get the safc to work with teh pressure sensor?

btw i have a total of 3 pressure sensors in my engine bay, greddy boost gauge sensor, apexi avcr pressure sensor and stock boost pressure sensor.

I have tried experimenting with the avcr pressure sensor, but at 0V i get -760mmHg, and at 5V i get 3.49 kg/cm^2 (i jumped the 5V power supply into the input to the avcr)

But if u plug the harness back to the pressure sensor for the avcr and take a reading for zero manifold pressure (engine stopped, but car is in on position) the reading is 0 mmHG = 1.508V.

if you try to plot these three points... 0 mmHG is way off the line if i were to connect -760mmhg and 3.49 kg/cm^2 (btw i converted all values to kg/cm^2 for excel)

so?

i'm lost... i think i'm going to give up soon.