Sorry for double post here, i posted at teamfc3s.org as well...

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: (https://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.

 

ouch, I can't think of anything to add, but I'm dumbfounded as well.

I guess it's microtech afterall.

You could always get the aftermarket boost pressure sensor that is listed on the DSM help page that has the write up on hooking the safc to where it's booost dependant....let me look for the link

 

I can see why the S4's narrow-range TPS causes problems, but since you have an S5, why don't you just connect the S-AFC to the output of the full-range TPS like you're supposed to? I'm sure it would work better installed the way it was designed for. Just a thought.

 

DSM boys have been doing it for years. It just makes more sense to me if you set your hi and lo positions off of boost instead of TPS.

 

Jason,

I could always do that... but i still think the safc can be better utilized for boost application.

So for boost levels under 8.2 psi, i can let the stock computer figures things out... When i pull the cat and put in a cone it will creep to 10 psi.

For teh extra 1.8 psi i can get the safc to control this.

Set safc lo throttle to be 74% (8.2 psi) and set 100% as hi throttle. so between 8.2 psig to 15 psig the safc can add more fuel at rpm points.

Which is perfect.

If i were to use TPS instead, i could be at 100% throttle and be boosting only 5 psi in 1st gear, or i could be creeping to 10 psi in 5th with only 50% throttle applied.
how is the safc suppose to tune for that... it would be weirld.

At this point the only person i know who did it was Dale Clark, hopefully he comes and replies.

What i think is that the safc isn't calibrated against the 5V output correctly, since i can run the pressure sensor for -15psi to + 15 psig, i'm going to see if i can find a compressor and a check valve and see what i can do.

 

What did you set the input sensor type to in the SAFC? If its set for some type of AFM it will be expecting a non-linear input.

Henrik
87TII

 

you need to go do a couple full throttle runs. then it'll make your max boost = 100%. it's the same for the TPS. at first 50% throttle = 100%. press it a few times and it learns itself and sets 100=100.

you need to teach it.

 

thanks scott, i had a suspecion (SP?) that teh safc wasn't calibrating properly

Henrik: The input sensor tupe has nothing to do with the TPS input, However i did set it at 06 06 if you were wondering. and increasing throttle and 4 cylinder ofcourse

 

Doh, of course. late night....

Henrik
87TII