Ok, I'm fed up with the current setup on my FC and I need some sort of guidance or suggestions.

I have an '86 GXL, and am running an SAFC. When I originally installed the unit I hooked it up to the narrow range TPS and tuned as much as I could. Of course we all know the limitations of that set up, so after a ton of searching and PM's I changed it around.

Step 2 was to remove the SAFC's TPS wire and run it to the pressure sensor, as this was supposed to give me the full range I needed. Well, it has been a headache. I see 20% throttle at idle, and as soon as I touch the throttle it dips down to 0% then rises unevenly as I apply more throttle - never reaching 100%. This makes it more of a PITA to tune - not saying it's not possible, just not perfect and one more thing to work around. I want to have it right. Is this simply a problem with the pressure sensor?

Ideally I'd like a full range TPS on my car. Is that possible with the stock S4 computer? Can I retrofit an S5 TPS onto the car? I've been toying with the idea of fabbing up a secondary braket and wiring to have the S5 TPS run just the throttle position for the SAFC and leave the S4 TPS as it. This just seems like overkill though.

So What are my options? How can I get my SAFC reading true throttle positions? Is there an aftermarket TPS available? Would an aftermarket MAP sensor give me better readinga than the one in the car? If so which one?

While I know many of you will say "just use the S4 TPS - it's good enough for what you need", I'd rather not. If I am going to go to the time and expense of installing and tuning the SAFC, I'd like to have it right. Be it totally necessary or not.

Thanks guys!

 

Ok, if a full range TPS is not an option, then what about an aftermarket pressure sensor?

 

you can put an s5 throttle body on there. the s5's narrow range goes to the s4 ecu, the full range goes to the safc. you do have to put the metering pump rod dealio on the s5 tb, theres room, mazda put a spacer in there.

 

And your tps sounds like it's scrogged imho.

 

The TPS is fine - it isn't what was giving me those weird readings - it was the pressure sensor. the TPS works like it should, but the narrow range is the issue.

Maybe the Pressure sensor is bad.....

The S5 throttle body idea seems like more work than wiring up a dedicated S5 TPS for the SAFC to the car. I guess an S5 TPS wont work on an S4 computer huh?

Anyone tried ?

Any other thoughts?

 

it seems to me that the SAFC needs to be calibrated??? I am unfamiliar with SAFC, but does it have a calibration feature????

 

sounds like the pressure sensor is reading wacky, it should only go up to near 100% throttle on hard accel not dip down first. idling at 20% would be normal as the vacuum will be at around 16"Hg at idle but will dip down to 25"Hg on hard decel. this is a guess but i would set the LO throttle input at 20%(idle) and HI throttle input at 100%(WOT) so it will ignore the hard decel for tuning. the map sensor will not always be a linear signal but it should still be fairly accurate for tuning so ignore the spikes in the signal and pay attention to the AFR and where your foot is instead.

 

Unless I misunderstood, that seems like more of a "work around" for the problem than it is a solution. Am I wrong?

While I know the map sensor won't always be a linear reading, I was hoping for some measure of accuracy better than I am getting.

 

Ok, if I were to take an S5 TPS and use it as a dedicated TPS for the SAFC - is there a certain way it would have to be wired up? Would I need to use a relay?

 

the s4 and s5 tb's are really only different in the way the tps mounts. you cannot bolt an s5 tps to the s4 throttle body.

 

Sure, it wont be plug and play. But could you not fab up a braket to mount it to the S4 Throttle body? And if I kept the S4 TPS on the TB and used the S5 TPS solely for the SAFC, I could mount it anywhere really - either under the hood or at the pedal end.

And here's the big question - lets say we solve the mounting issue, and it fits properly on the TB - will a full range S5 TPS be compatible with the S4 Computer? Will the ECU just ignore the full range of signals and work as normal? Could I just use the full range S5 TPS in place of the S4 one - assuming I get ti mounted properly?

 

Nick86, I too have been considering this modification and heres what I have found so far, the s5 tps is actually 2 tps sensors, a short range and long range. essentially there are 3 wires to each tps, power, ground, and signal. they share power and ground and have 2 seperate outputs one narrow and one full range. so after retrofitting, and it sounds like the entire throttlebody is easier then just the sensor, you would need to adapt your oil metering pump to it and rewire, sending just the narrow range signal back to the s4 ecu and the full range to your safc. The s4 ecu is calibrated only for the narrow range signal. Also the s6 fd sensor works similiar except that it is 1 individual sensor with 2 seperate outputs unlike the s5 which consists of 2 seperate s4-looking tps sensors. Hope that helps.

 

It looks like the pressure sensor signal is working.
Like BASTARD suggested, you may need to do a calibration.
The NA should show 90-100% (atmospheric) with the key on & engine off, then drop to ~10% at light throttle cruise.

 

Thanks man!
I am amazed that it is considered easier to swap TB's than just adapt the TPS!
Does the S5 TPS actually have 2 seperate plungers?
Have you done this on your car yet?

I'd love to know if the narrow range portion of the S5 TPS is the same as the S4 unit - ie if I were to use the narrow range portion of the S5 TPS for the Stock ECU - would the ECU accept that signal? Is it identical to what I would have gotten from the S4 unit? If so I could just use that for the stock ecu and the full range one for the SAFC.

Maybe the FD one would be more appropriate.

Would this work? Thanks for the info!

 

The S5 narrow range TPS gives the same signal as the S4 TPS.
The S5 wide range TPS uses the same sensor plunger, giving the same signal range, but it rides on a linear cam instead of a lever.

 

yes the s5 unit actually has 2 plungers, no I havent dont this on my own car yet but will be in the very near future (as soon as i find a s5 throttle body and or s6 full intake setup for a good price). yes the s5 narrow signal is the same as the only s4 signal, and the s6 one works the same only one unit and plunger with 4 wires, power grnd narrow and full. but again mounting may be difficult.

 

Ok, so theoretically it could work like this:

I replace the S4 TPS with the S5 Unit. (Of course it isn't just a plug and play but lets put mounting issues aside for a second.)

The Single plunger on the S5 TPS will be activated by the throttle just as the S4 unit was.

The narrow range wire from the S5 TPS will plug into the stock S4 harness wire that goes to the S4 ECU providing the ECU the narrow range it needs.

Then I'd run the full range output wire from the S5 TPS straight to the TPS input wire for the SAFC.

This would give the Stock ECU the narrow range needed, and give the SAFC an accurate linear full range throttle position. Right?

If so, that would be a great solution!

Has anyone done something similar - be it with an S4 or S5 TB?

Thanks again guys!

 

I have an s4 N/A with a wideband and safc (until very recently anyway, i'm in between computers at the moment and waiting for rtek 2.0). I think you are wasting your time because the SAFC doesn't have the capability to tune the car around town much anyway--but that doesn't matter because the stock ECU does a good job around town. Are you running a wideband? Do you truly understand what effect the SAFC will have on this car on the street?

Are you hoping to tune AFR's under part throttle? If your stock O2 sensor is working properly, you will be in closed loop EGO feedback. Being one of the only guys on here with a wideband on an n/a, it has made me realize just how good of a job the stock ECU does with the fuel map, except perhaps under WOT where it of course goes rich. When you are driving around town and on the highway most of the time your AFR's are bouncing between 14 and 15:1 on the stock ECU. This is where you want them to be. When I was running a Megasquirt I had a hard time even getting the car to do this.

Before my wideband, I used to lean out the SAFC on the highway (in the 100% map and in the partial throttle map) thinking that it would get me better gas mileage. Once I put the wideband in I realized that it doesn't do ****, and it shouldn't. The stock ECU is smart enough to use O2 feedback correctly and bypass corrections you make with the SAFC to the AFM signal. Regardless of how you set your SAFC, When the car is warmed up it will stay near stoich throughout your driving provided that the ECU does not have to use accel enrichments or decel fuel cut.

When you mash the throttle suddenly, on the stock ECU the car is not going to bog or hesitate. It will hit perhaps 13's as the throttle is opened. On an n/a, the stock ECU handles accel enrichments and decel fuel cuts pretty well without any kind of piggyback necessary. It took me a long time to get this tuned on a Megasquirt and honestly it was still not as good as what the stock ECU could do. You can't really tune accel enrichments on an SAFC anyway.

Those are the only two things you would want to use a full-range TPS for: round-town cruising, which the stock ECU handles well using closed loop O2 feedback, and accel enrichments, which the stock ECU does a pretty good job with anyway. The full range TPS is most useful for an electronic OMP, which is a POS anyway.

Get the thing dialed in under WOT using a wideband and leave everything else alone. You are wasting your time. There is this myth out there at the stock ECU sucks at everything. It of course has its limits (especially on a T2), but it does idling and driveability very well. When I was tuning my Megasquirt, most of the time I spent was trying to get the car to run as well in normal driving as it did on the stock ECU. I got the WOT AFR's tuned pretty easily on a dyno, and they were mostly better than what I could do on an SAFC. You don't realize any of this stuff until you try and tune all the aspects of EFI yourself.

 

The S5 TPS will not plug into the S4 harness. Two different plugs

 

That is because your electrical system has problems, remember?

 

ARGHX's point is well taken.
All cruising is in closed loop where the S-AFC is ingored.
The only area you can tune is medium to full acceleration.
It's a bigger deal on a turbo than an NA.

 

FWIW- Here's something that often gets overlooked.
It may not be a factor with NA's but it sure is with tuned up turbo's.
There is a point in WOT where the AFM hits 100% before you hit the red line.
Mine used to hit 100% AFM before 5K.
Above that the ECU is essentially speed/density mapping.
In that area, the S-AFC's RPM & correction settings still apply.
Last spring I found a Cosmo AFM which gave linear values up to 6K @ 12PSI.
I couldn't tell any difference in performance, but the S-AFC tuning was different.

 

As SureShot said, point well taken.
While I realize that the benefits gained through all this may be outweighed by the time and effort involved, I am still interested in persuing it. This whole exercise was never about ultimate power or mileage for me. Realistically it's about getting this setup to work as it is intended to - to the best of my abilities. Of course having a full range TPS on the car wont make a ton of difference - but I'm stil interested in trying to get it tuned without any work arounds. I guess it's just my stubborness coming through!

The car will be tuned with a wideband too. Still haven't decided if it will be on the dyno or street though.



No, I know. I used the term "plug" merely as a simplification of the process. I intend to remove the OEM plugs from both ends and replace them with a matching unit.

 

I agree with ARGHX on the whole. I put my old SAFC on my 86 na and just used the tps as the high low. I set the low at 99 and high at 100 and went from there.

I set the high and low to the same values thru the full rpm range. It has something like 25 percent removed above five grand for high and low and below that I have 15 percent removed thru the full range .

With the 02 disconnected I see cruising along at three grand afr in the 15-15.8 range. Shove the pedal to WOT and on the whole the afr goes to the 12.5 range and usually gets closer to 12afr around six grand and up. That's from memory.

I've played with a minus 30 above five grand and minus 25 below.

As for consistent afr I'm fairly sure you need to duplicate the load. Load such as going up the same steep grade time and again. If you drive just on a straight stretch of road I think the afr will change to being a touch leaner than the uphill stretch you just drove. Sorta common sense thing.

The afm and it's condition is a big factor b/t different cars, that's a given.

And, depending on the altitude you live at, removing the plug from the atmospheric pressure sensor WILL make a very noticable difference in the afr thru the full range. I live at, and I'm guessing, about 700ft above sealevel. I've had that plug off and seen the afr and then put the plug back on and it's very noticable. Goes richer with the plug off. Talking series four cars, NOT S5 with their built into the ECU atmospheric pressure sensor.

I accept that I don't know much of anything about tuning, but ARGHX observations ring a bell. At least for the na cars. Turbo's a bit diff.

 

+1

At least that's what I remembered from this thread: https://www.rx7club.com/showthread.p...ght=megasquirt