Jeff_Ciesielski

OK, so I bought myself a motorola mpx4250a map sensor, Wired it up in a project box, and have it sitting here waiting to be installed. Problem is, I am unsure what wires to tap into on the stock pressure sensor. I dont know which wires are ground and which are power. The Haynes manual is completely useless. Any clues?

NZConvertible

Why are you tapping another MAP sensor into the stock one? That doesn't make any sense.

This wiring diagram shows the MAP sensor. BR/W is Vref (5V), BR/B is ground and G/B is signal.

http://i8.photobucket.com/albums/a47.../NA-ECUTwo.jpg

Jeff_Ciesielski

Sorry if I was unclear, I'm tapping its power and grounds.

RETed

Would help if you tell us what year RX-7 you got?
1986 - 1988 versus 1989 - 1991 have different wires.
One set has +12VDC, +5VDC, signal, ground.
The other has +5VDC, signal, ground.


-Ted

NZConvertible

Sig says 91.

Still not sure why this is being done. Curious.

Jeff_Ciesielski

http://www.2gnt.com/www/corbin/foolafc.html

I want to get a stable voltage for the sensor by reading from the stock location, then run the output to my safc. I have an NA. However, this now seems to be a moot point, as I tapped the power and ground at the ecu, and the sensor reads 5v at atmospheric pressure. Something is obviously wrong

NZConvertible

Using the MAP sensor signal instead of the TPS signal is fairly comon, but the way you're doing it seems totally pointless. Tapping the S-AFC's thottle position wire into the MAP sensor wire at the ECU would give you exactly the same result without buying a new sensor or running a single extra wire.

Jeff_Ciesielski

It wouldn't give the same result. The NA MAP sensor doesn't read much into boost. I wanted to be able to have a boost dependent map

~edit--I realized that I didn't specify. I turbocharged my 91 NA. Which is why I cant use the stock sensor. Stupid me :/

NZConvertible

Yeah, those little details often help...

Since you've got an S5 with a full-range TPS you could save yourself a lot of hassle by just hooking it up the way it's supposed to be. I don't really see any reason why using the MAP sensor instead of the TPS will give you a better result. The auther of the link you're following can't even expalin why. He just says "I think that boost pressure is probably more important as an indication of how much air is coming in." Apexi could've decided to use either sensor but probably picked the TPS after R&D showed it to do the job better. The only reason I see for using the MAP sensor is if you had an S4, which only has a narrow-range TPS.

Jeff_Ciesielski

Unfortunately, as I am a poor college student, I'm having to tune the car myself without the help of a dyno (i'll soon have a wideband on the way). So for me at least, tuning by boost just makes more sense. As I can lean the car out about 20-27% off boost, and then just lean out the car where needed on boost ( i also have an 8:1 FMU which will richen up on boost..FYI). I've tried throttle based tuning, and it just seems like too much guess work...or maybe I just suck at it.

ErixHvn

Don't get discouraged man, I'm doing something similar to you but I will be trying to supercharge my 86 NA sport. The S4 tps wont be used for the signal to the SAFC on mine but I was also hoping to use the same leads off the press. sensor and piggyback maybe a TII sensor instead. Then run that lead to the SAFC.
Matter of fact there's a thread on the SAFC forum regarding this.

Jeff_Ciesielski

I noticed that there is a thread in the SAFC forum, but they never talked about which leads to use. That forum seems somewhat dead come to think of it.

NZConvertible

Remember that this is a not a standalone being tuned from scratch. All you're doing is retuning the factory fuel curves. The stock maps already run the engine leaner in cruise and richer under load. The AFM is still the primary load sensor. Whether you use the TPS or MAP sensor input, the S-AFC's "throttle" setting simply determines which of the two correction curves are being used (or somewhere in-between). The amount of fuel added is still mainly dependant on the amount of correction you dial in.

Anyway, did you get the Motorola sensor working? According to the data sheet if you put 5V in you should get 2V out at atmospheric pressure. Check that the voltage across the Vs and Gnd leads actually is 5V.

Jeff_Ciesielski

to answer your question, no, I havn't gotten the sensor working yet. According to the data sheet, there are 3 possible configurations for the pins on the sensor I have, and I havn't had the time to test all three yet.

ErixHvn

Any luck using this sensor? I might wind up having to go this route too if I cant find a way to piggyback a TII sensor instead.