Nick86

iTrader: (1)

In March I got myself an S-AFC (4 button blue screen one) for my car - an 86 GXL. Since then I have searched, and read post after post about installing and setting them up - but the main question I had never really got answered, so I've had to start a thread.

The vast majority of SAFC Installations on FC's that I have read about have been on S%'s, and some S4's, but mostly TII's. But my situation involves an S4 N/A. Being an S4, there is the issue that the throttle seems to read 100% after about a quarter throttle. I know that the S5 TPS is full range, and those who have TII's use the pressure sensor - but what can I do?

Is there a way that I can install the S-AFC where the throttle readings will be accurate? While I recognize that it may be difficult, I'm looking for proven methods here. Thanks for your suggestions!

ddub

I have it on my s4, and thats just the way it's going to be. You can't really do anything about it, that I know of.

Jaared

could you not just put it to the pressure sensor and set the change over where you want it... seems the stock fuel system can handle it fine till your really on it... not just mashing tha gas for a second like the tps reading change over would do.

Im not sure but id guess a vaccume gauge in a na would act alot like a turbo car.... until the boost came on of course...

Nick86

iTrader: (1)

I wondered about the pressure sensor, but how accurate is it? Is it worth hooking it up like that, or will the readings be just as mangled as with the stock S4 TPS?


Is it even worth trying to get around this issue, or does it not have any real effect on the proper tuning of the car? If I am going go to the trouble and expense to take the car to get it tuned on a dyno with a wideband O2, I want to be sure that I can get the best out of it.

ddub

Well, when you're on the dyno doing your run getting your air fuel ratios, you're at WOT right? And that's what you tune for, max power at WOT... Well, even if it shows 100% earlier because of the way the s4 is set up, when you're at WOT, it'll still be tuned accordingly. It's just, when you are not at WOT but it is still reading 100%, it will be taking the corrections for that rpm range.

Jaared

that that could mean adding or taking away fuel where its not needed. if your change over is set to 99/100 and that happends at 33% throttle then your WOT all out run map will be used for lots of times when the low map would be best.

It seems like the pressure sensor would give you more room for adjustment... but then again im a turbo guy.

89GTUs Lady

Doesn't work for NA cars. The output from the NA pressure sensor is a very narrow reading because the vacuum reading on NA cars is constant while the engine is running.

the pressure sensor and S-AFC works for TII's because the pressure sensor sees a much larger range of voltages due to the boost always rising and falling.

89GTUs Lady

Sounds about right. When tuning the S-AFC on the dyno, you're only using the high map anyway.

The only downside to using the AFC on an S4 low range TPS is that you spend most of the time on the high map. If you're adding fuel with the AFC, this will lower your gas mileage. Otherwise it works just fine.

Aaron Cake

iTrader: (1)

You could always install a full range TPS from either the S5 or other car.

This thread has info on using the pressure sensor:
https://www.rx7club.com/showthread.p...hreadid=202098

The NA boost sensor (according to Mazda, the NA has a boost sensor, the TII has a pressure sensor...go figure) will read accurately enough in an NA application to be used with the S-AFC. However, it is much better to obtain an aftermarket vacuum/boost sensor if you plan on doing this.

Nick86

iTrader: (1)

Thanks Aaron - but I think you have the wrong thread there!

If I am going to go out and buy an aftermarket piece, would a boost sensor be the best way to do this? If so - where would I pick one up, are they universal, and how much money are we looking at here?

89GTUs Lady

I don't disagree with you here. The NA Boost sensor output is not the problem. The problem is that the car is always in vacuum, so the output from the sensor is always the same.

In a TII the pressure sensor sees boost and vacuum, so the output varries. the S-AFC can be set to use the High map when in boost and the low lap when in vacuum. On an NA, you'll only ever get one map.

Aaron Cake

iTrader: (1)

Summit Racing. These sensors are made by Crane, MSD, etc.

Um, we're talking about an NA, correct? So obviously the NA boost sensor will always read vacuum. But it will read varying degrees of vacuum based on engine load. Hence, you can now tune the S-AFC to load instead of throttle position.

I assure you that the NA boost sensor puts out a voltage based on the amount of vacuum it sees.

89GTUs Lady

It sounds great in theory, but does not work in practice. The output of the NA boost sensor (while in vacuum) is in such a narrow range that the S-AFC sees the signal as 0% thottle at all times.

Aaron Cake

iTrader: (1)

I'll be happy to go home and prove this. I did quite a bit of work with the NA boost sensor when I did my turbo-NA project. I don't remember the actual values, but the output swung by several volts as I sucked down a vacuum. If I have time tonight, I'll put my scope on it again and repeat the test then post the values tomorrow.

Regardless, it's still a much better idea to use an aftermarket sensor.

Nick86

iTrader: (1)

MSD-2311 MAP Sensor, 1-Bar, normally aspirated applications Today $38.99

Is that what I'm looking for?

So, if I were to go out and pay $40-$60 USD for a Crane/MSD MAP sensor - would it be worth it? Would I then be able to accurately tune the SAFC throughout the throttle range? Or would picking up a used S5 TPS and get creative with the mounting/wiring of that be a better option? Does it accomplish the same thing - or would one be superior to the other?

89GTUs Lady

Using a vac-pump will prove your theory. The only way to really test this is to drive around with the car under load and a monitor the output of the NA Boost sensor. I know where your coming from, but it just wouldn't work for us.

I may have to explore the aftermarket sensor.

Aaron Cake

iTrader: (1)

I just found my data! Wonderful having a VPN to your server at home...

OK, at atmospheric the sensor read 2.4V. Applying 10" of vacuum resulted in about 1.5V. I was using my tongue and a vacuum gauge, and 10" was all I could manage while holding the sensor, gauge, voltmeter and trying to tongue/suck a good vacuum (according to the guage, normally I am good for about 30"). I can only assume that the sensor voltage would continue to drop off until it hit about 1V. This is remarkably inverse to the TPS. If I am up for an adventure tonight I will try again as I now have a real vacuum pump.

WAYNE88N/A

you're right Aaron- with mine connected normally in the car, I can get about a 3v swing out the sensor- it doesn't act too linear, though, but then again I had no actual vac gage readings for comparison, it was kinda just "play with the throttle" type testing...

Aaron Cake

iTrader: (1)

Just to add more fuel to the fire:

I didn't get to checking a spare boost sensor last night (bar night), but I did find some posts by Bambam7 using the search. He did some testing with the NA boost sensor as well for his turbo-NA project.

This one shows voltage variation during vacuum:
https://www.rx7club.com/showthread.p...hreadid=262629

koukifc3s

iTrader: (3)

so what's the best way to plug it in?

End3r

I'd also really like to know!

koukifc3s

iTrader: (3)

I think that it should be fine with the S4 narrow TPS.
I mean if you're daily driving then you wont go past 3k much.

The most corrections on the fuel curve are after 4k RPMs so it doesnt really matter if you are using the hi throttle map when you're low thottle.

soccerspawn

Well I cant believe anyone with an FC would never drive it over 3k as a daily driver. Its not even healthy to drive an FC like an old lady. But that aside I have the same problem on my NA s4 safc setup. My problem with just leaving it is that you dont get any fuel economy out of yor safc. This results because you will be using your WOT map ALL the time. That is not conducive to fuel economy. I believe I am going to use the rpessure sensor, but I need to wait until I am done my midterms. If not I am going to install a boost sensor and try that. I am not going to dyno tune my car (though many people will disagree with me) I think driving tuning is better. Best case scenario the imppossible perfect dyno can only approach an acurate simulation of real world conditions. You will want to tune your safc at different throttle possitions for best power and fuel economy. If you only drive your car to 3000 rpm you should just leave it parked and take the bus. Nobody who doesnt go over 3 grand would bother buying a SAFC, prob not even an FC whats the fun in a rotary you dont rev?
Short answer, try the pressure sensor I am going to, it seems to be the easiest fix. I just want a semi accurate setting so I am using the proper fuel map, last time I looked you can set what the SAFC reads as high and low throttle readings.

koukifc3s

iTrader: (3)

im saying that when I drive on the streets, I dont go over 3k

and most people with SAFC lean it out in the lower RPMs, which still gives ya better mileage

and when its time to let it rip, such as on the freeway ramp, or on the track, believe me that SAFC will be worth it to me

drago86

The car isnt allways in vacume, at WOT there is no vacume, and between idle and WOT there are varying degrees of vacume, how do you think NA cars run with map sensor based ecu's? vacume is a very good indication of throttle position.