Hi,



I've been told instead of geting the stock S5 MAP sensor.. I could just get any 2 BAR OR 3 BAR Map sensor....



So I was looking at the Gm 2 and 3 Bar MAP sensors and I noticed they only take 3 wires, But the stock unit uses 4 wires....



Does anyone know how to wire up the GM unit...??? OR is the GM MAP even compatable...????



I have a feelling you guys have awsered this one before.. But I couldnt find the right thread....



Thanks guys!!!

 

Doesn't the stock unit have 3 wires also..?

 

stock s5 has 3 wires, although theres a spot for a 4th wire. the s4's use a 4 wire, the 4th wire is a 12v signal

 

Well that make a little more sence now!!! Neither chilton OR haynes repair manuals have a wiring diagram for the 3 wire S5 MAP sensor..



LOL... They show a diagram for a 87 and they say 86 is similar, Then they show a diagram for a 88 and say that the 89 is similar

Thats stupid, there both for a S4..

 

Where is the MAP on an S5?



GMs is a piezoresistive sensor.. I don't know if it's going to compute what the ECM wants.



Theres two types of piezo sensors out there used for MAPs. Piezoelectric and Piezoresistive. PE generates voltage from pressure, PR generates resistance from pressure.



Not sure what type the S5 one is.

 

In this wiring diagram I'm looking at it shows a resistense symbol inside of the MAP sensor with a BR/b and a BR/W conecting to it..



I would guess that the stock S5 sensor is a Piezoresistive sensor..



I guess ill need to get ahold of a gm wiring diagram to find out the pin out.. Unless one of you guys alread already know it???/

 

One is 5v and the other is ground, the 3rd signal wire is the output.. It connects directly also to the boost meter in the dcash, that makes me think its more piezovoltage..



Doesn't really matter I think, I think the ecu just wants to see a voltage output from the sensor..

 

OK. the stock S5 Map sensor has 3 wires

1. Brown/White- +5 volts



2. Green/Yellow- IS a ECU imput that puts out 1.8 - 2.2 Volts



3. Brown/Black witch is a Ground



Since the stock sensor puts out voltage it is Piezoelectric???



If it was a Piezoresistive sensor It would put out resistance???



Kinda sounds like a GM sensor wont work...

 

5 volts is reference voltage.



1.8 - 2.2 volts may be the result in voltage drop after walking through a PR circuit.



5 - 3 = computer witnesses 2 volts leftover which could only mean xx pressure is in the manifold.





A PE circuit could also produce 1.8v - 2.2v as output, but that seems a bit high for a sensor to produce all on it's own. I'm not positive on the output ranges of PR and PE sensors.



Since a MAP sensor takes a baro reading just before turn key for the ECM, why don't you feed the stock one 5 volts and a ground a measure the output, and then do the same thing to a GM sensor? You wouldn't have to install the sensors or anything, just bench test with 5 volts and a DMM to find out if the baro reading is actually the same or not. If it's not the same output in your controlled environment, it won't work on the car (properly, anyways).



I'd still be weary of the sensor not reacting to pressure in the same manner for the ECM to comprehend, that's the difference between 2bar and 3bar MAP sensors. The composite inside has changed to be more or less sensitive to change over the same voltage range for the ECM. But that doesn't mean it won't work. Everything might be all lined up correctly to work the same. It just seems like slim chances / not worth the effort (unless you're installing a standalone, which has alot more versatility than an OEM ECU).

 

Well I'm trying to do a turbo II swap into my FB.. And I'm having problems finding a S5 Map sensor for a ok price...

And I recall asking about map sensors on this forum once before, and I think a global charter moderator told me tat any 2 Bar Map sensor would work.



I'm goin to search for the old thread and see if I can find the guy that told me that.....