ExFastWS6

i need to know if i have a 3 bar or two bar map sensor? i know for sure that there is a map sensor behind the thrttlebody that says mazda on it. i guess its a two bar? where do i get a 3 bar and how much and whats required to install... i fell pretty dumb rigt about now having run 1.6 bar before on accident on this sensor if its a 2 bar

wonder1and

have you replaced it? if not... its a 2 bar

ExFastWS6

i bought the car with most everything already installed...and the owner didnt have a list of what all had been done.. basically my dumbass had teh job of sorting out everything when i was given a car that had a t78, rebuilt 3mm apexed and street ported motor, and full electronics and intake and exhaust and have had the pleasure of buying the car and know JACK **** about rotaries, turbos, avc-r's, power fc's, etc, etc and getting the car from running liek it had 330hp to feeling liek its got 550. boost leaks, miles of vacuum hose, and **** poor tuning led to a crash course of learning.. so i have no clue whats what mostly on teh car lol... sad really. but only one way to learn.

mr2loser

you could always check the voltage of the MAP at idle and at 1 BAR (ie with the car off but still getting its 5v referenve and reading atmospheric pressure).

then refer to repair manual and see that your numbers are right.

greg

sub-zero

The GM 3 bar sensor is larger then the Mazda and the factory map sensor says (Mazda map sensor) or pressure sensor on it.

duboisr

Question-- is the stock map sensor 2 bar, or is it 1.2 bar ? I understood it is 1.2 bar ,, please teach me .

mr2loser

OK, MAP means Manifold ABSOLUTE Pressure. Since it's ABSOLUTE, it uses one whole bar (and Bar just means atmospheres or groups of 14.696psi's) to read perfect vacuum to atmospheric pressure (~30"hg - 0"hg, or negative 14.696psi - 0psi). So, if the sensor were a 1.2 Bar we'd only have .2 bar or 3psi left before ran out of sensing range. And we know that's not the case with these Mazda sensors.

Thusly, a 2.0 Bar sensor would allow the ECU to see 14.7psi before it read the highest possible voltage and did its programmed thing which might be fuel cut.

Similarly, 3.0 Bar sensors allow nearly 30psi of boost. Making sense?

The way they work is that they have a little diaphragm in them that is sensitive to pressure. The pressure tends to stretch the diaphragm, like pushing on a drum head. The diaphragm is mounted, if you will, to the body of the sensor via piezoelectrics (i think). These translate the stretch (and hence the applied pressure) into voltage.

So, if one wanted, one could have a MAP sensor made in any "Bars" he wanted. In fact I've seen them on Ebay up to 100psi and in aftermarket ECU kits for 4.5 Bar (~51.5psi boost). It's just a matter of calibrating the internal electronics over the standard 0.5 to 4.5 V range. So when we say "2 Bar" and "3 Bar" we are just abreviating. These sensors, from Mazda to Toyota to GM are all a little different. The Mkiii RX7 might be 2.2 Bars over its normal range of .5volts to 4.5volts. Where maybe a toyota MR2 one is like 1.8 Bars. Just giving examples here.

The only way to know for sure what the true range a sensor is, is to take it and apply 5 Volts and a ground to it. Then apply different pressures to it, from 20"hg, to 0psi, to 10 or 15psi. plot the pressures versus output (or reference) voltages against each other on a little graph. You'll find that the voltage change is very nearly linear with pressure increase. So one could interpolate the high boost voltage knowing only vacuum and atmospheric voltages.

Man, I've rambled.
Greg

FDokinawa

iTrader: (5)

mr2loser.. good info. Here's another question for you or anyone else out there. How does "Bar" relate to "kilos". I know I cant go very far over 1 kilo on the stock MAP sensor. So is one bar equal to one kilo is pretty much what Im asking....

mr2loser

you mean kg/cm^2?
somebody check my math here, but it seems that 14.7psi (1 Bar, 1 Atmo) =~ 1.036kg/cm squared.

So maybe 1.20kg/cm^2 is reasonable since I read that guys hit ~17psi.

Greg

duboisr

mr2 loser, so you must count both pos and negitive pressures . Thank you I think I got it now ( may be ) .

GoodfellaFD3S

iTrader: (213)

From one soldier stranded in Iraq to another :

1 bar=14.5 psi
1 kg/cm^2=14.22 psi

This is a great link to reference:

http://www.speckdesign.com/Tpressure.html

Note that in the above link kg/cm^2 is listed as "technical atmosphere," or 1 kgf/cm-cm.