gsracer

Ok so I finally get everything set up on the safc. I run a line from the cabin through the firewall around the IC and down to the pressure sensor. I taped into the brown/red wire before the fcd. I turn on the car and hope for the best....and I actually am getting numbers. However I reach 100 percent around .4bar...or I guess 6psi. This is what I would be running stock, but I've heard from a few places that the pressure sensor reads from -15 psi all the way to 15psi, and the corresponding voltages would read from 0-5 volts.

I've heard you need to do a few WOT runs to set the car, but after running up and down the highway under boost and vacuum for 20 minutes I'm still getting the same results. With the key in the on position I'm getting 67 percent throttle. If the pressure sensor read from 0-5 volts from -15 psi to 15 psi I would think it should have shown 50 percent. Hmmm....well this got me thinking. Really until about 8psi I want to stock computer to do it's thing, and after this it'll switch to my settings via the safc. However at 4psi it's reading 100 percent.

My idea is to run a resistor between the safc and the votage I'm seeing from the pressure sensor. If I run a resitor the voltage the safc is seeing would drop, but the voltage would still increase and decrease linearly. If I did this 100 percent on the safc would theorettically increase to a higher pressure, and I could then set my hi-thrtle setting at 8psi. However this is all assuming that at 6psi I really am getting 5 volts from the pressure sensor and there isn't some unseen error I haven't accounted for.

For all the e6k/mt8 ****'s...I'll be going stand alone as soon as my funds permit it, but this will have to do for now. My a/f ratios are fine as it is, so I'm not in any danger of hurting the engine. Just looking for any sort of input.

SwooshMan

Will this work on a n/a?

Rotary Racer

Swoosh: There is no need to do this on an N/A, due to the lack of a turbo bolted to the exhaust .

GSR: Your idea is interesting and I like people who think outside of the box and try something different. But do you think the benefits from changing over the SAFC's view from the TPS to the Pressure/Boost sensor (for the activation of the new fuel curve) will out weigh all the pain your working through now? Just seems to me that if using the pressure sensor was a better solution Apexi would have done that instead. Just wondering.

- Dana

SwooshMan

Having a turbo has nothing to do with how you wire a S-AFC!

The reason us S4 owners are trying new ways to wire the s-afc is because the stock tps reads 100% throttle at about 1/3 of the actual throttle. Therefore it makes it very difficult to actually tune it with a high and low throttle map.

J-Rat

iTrader: (2)

Did you zero out the SAFC before you changed to the Pressure sensor?

gsracer

the map's were all at 0.

using the pressure sensor is nothing new, dsm and turbo s13/s14's have been doing it for a while.

J-Rat

iTrader: (2)

What I mean was..Did you initialize the SAFC?

Scott 89t2

I really don't see the big deal about using the pressure sensor. it's just not going to make much if any diff.

first of all between S4 and S5. tunning for full throttle is the exact same. there is no disadvantage having the S4 tps.

the ONLY downside to having the S4 tps. is while crusing over 4000rpm AND over 33% throttle. your gas millage will be a bit lower then if you had an S5 tps.

but who the hell crusies like that?

and the S4 worse gas millage is only lower if your high and low settings are different. mine are the exact same. I could unplug my TPS from the S-afc and my WOT, idle, and cruising gas use would be the exact same as with it pluged in.

gsracer

I initially set it up via the pressure sensor and not the TPS sensor, I never tried the TPS sensor.

Scott I don't think using the pressure sensor is any magical thing but I definitely think it's better than using the TPS. I think it's just easier to set up. Under 9 pounds I let the stock computer figure it out. Over 9 and it switches to hi-throttle maps which 99 percent of the time means I'm going WOT by then. We all know that under 3800 when the secondaries come online can be a dangerous place for those running higher boost pressures even on the stock turbo.

With it set up via the pressure sensor anything exceeding whatever limit you set (I have it around fuel cut) you can start adding in more fuel to the primaries. The primaries are maxed out already, but adding in 720 primaries isn't a problem. Lean them out to stock injector levels on the low map, and add fuel as neccesary for the hi-thrtl maps.

Fuel unfortunately is only one part of the equation. I really don't know of too many alternatives for ignition timing beyond re tuned stock ecu's and stand alones.

jacobcartmill

iTrader: (6)

i have my safc wired to the widerange TPS on my S5. i am running ~12 lbs on my stock 550's which requires about 40-45% more airflow correction to ge the AFR's in the 11's. all is well... HOWEVER, when you are running +50% on an safc wired through the TPS, when you slam the gas to the floor, it instantly adds +50% airflow which totally dumps fuel all at once. in order to compensate for this i have just been "easing" into the throttle instead of flooring it. this compensation is not nice to turbo spoolage. if i were to have my safc wired to the pressure sensor (thinking it were receiving a TPS signal when its really the pressure sensor signal) then i could slam the throttle, have the turbo spool up, and have the SAFC add fuel when it actually needs to be there, not before the turbo is spooled...

Jaared

good point.

HAILERS

&&&&assuming that at 6psi I really am getting 5 volts from the pressure sensor and there isn't some unseen error I haven't accounted for. ######

I'm probably misreading and misunderstanding most all this thread (hey! I new at this).........but I really, really, really, really, really don't think you'll ever see five volts on that safc, much less at 5 psi.

The most output voltage I've ever seen being put out by the boost/presure sensor is close to 4.10 volts and I had to use a MITTYVAC to see that and the clincher is the Mittyvac I have only put out 12Psi and when putting vac on the sensor I can't get the sensor to read less than .125 volts.

So anyway, after putting as much vac on the senor as I could and as much pressure on the sensor as I could with the MittyVac, I get a reading of 53 percent with the key to ON and the engine OFF.

I say buy a MittyVac or equivalant for twenty bucks or ??? Down deep inside I want to say *the percent number is *just a number to relate to*, but I won't. Might be wrong somehow.

Tell you what, if you have a series four, push the vane all the way open in the afm. Do you see 100 percent on the afm???? I'd bet money you won't see 100 percent. Maybe 90 to 93 percent max. What do you show on your safc??????????????????????? This question is not really related to any of the above.

totallimmortal

A pressure sensor would never read boost on an NA so it would never add fuel, right?

Aaron Cake

iTrader: (1)

When I was playing around with this, I used an aftermarket boost sensor. Don't remember what exactly it was (I borrowed it), but most of the CDI box vendors (Crane, MSD, etc.) will sell an appropriate sensor. You will also want to set the S-AFC so that the TPS arrow is up and to the right (if I am remembering correctly).

Not a lot of advantage to doing this in an NA.

jacobcartmill

iTrader: (6)

so set the throttle points on the SAFC lower to compensate. that way you can get 100% "throttle" reading by getting like a 3.x volt signal from the pressure sensor (instead of the 5v or whatever you get from 100% tps voltage)

so lets say your safc reads 30% throttle by the time your pressure sensor is putting out the voltage for 5psi... set the SAFC to add however much fuel you need at 30%... so make the hi throttle point 30% and the low throttle 0%.

Jaared

i have a boost activated switch i got for a custom water injection setup i never went through with.

Anyway why couldnt i set the boost switch to 8 psi and hook the safc to it. so at under 8psi it will see 0 and at 8/9 it would switch on and see 100 and switch to the high map.

am i all off base or would this work? Can the safc tps/pressure wire take 12volts imput?

jacobcartmill

iTrader: (6)

it MAY be able to take 12 volts but it would definitely be pegged at 100%. i'm not sure if it can handle that much voltage though.

Roy James

Im not sure but i think the TPS wire is a 5VREF signal.

HAILERS

Why don't you just look at your SAFC and your boost gauge? When the boost gauge sees 8 psi you take a gander at the SAFC percent, and take note of that percent. Then stop the car, go to SETTINGS, go to TH-POINT and enter the above noted percent as to where you Hi-Throttle begins???????? And set the LO-Throttle for everything below that OR set the low throttle at some point lower and the SAFC will interpolate the setting b/t that low point and where the Hi point is.

The fuel is added or subtracted by the rpms...for what it's worth.

jacobcartmill

iTrader: (6)

thats what i was trying to say way above

Jaared

is this assuming that the safc is hooked to the boost senor or the tps?

i guess i was looking for a way to make the thing see 0% till 8psi and then go 100% like a switch. below 8psi the stock ecu settings should be ok....

the boost switch i have just completes the circuit at what ever boost you set it to. where would i get a "5vref" or what ever source. this just seems like a way to take the guess work and test and tune out of the whole thing.

gsracer

Yes, that's if you hook it up to the pressure sensor. In all honesty it doesn't matter what percentage the pressure sensor is sending out, as long as it's under 5 volts when you want to have it switch from the hi-thrtle to the low thrtle.

That's basically what hailers is saying. Hook it up to the pressure sensor, look at what the TPS percentage says when you around around 8-9 pounds, then use that percentage as the switch point between high and low maps. Whether this is at 70 percent or 99 percent, it really has no effect on anything.

Jaared

i thought you were getting 100% at 6psi..... thats what your first post said.... right?

gsracer

It was originally, but you have to put the safc has to learn the range of voltages it's going to see. After making a few WOT runs, 100 percent was happening a little later. I put a few resistors inline between the pressure sensor and the safc to lower the voltage even more so I had a greater range to adjust the switch.