MAP Sensors

Good technical discussion, what I was actually trying to lead people to with this discussion about map sensors is what the difference was in how people treat things. for example, most people would refer to the state of NA as negative manifold pressure or a vacuum. For most tuners, its anything below 100kpa, 14.7psi absolute, less than 1000mbar, but I was trying to get the point across that they are all the same thing, and when most people describe something as vacuum, I prefer to call it a little pressure ;)

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Originally Posted by ECU-MAN

some Hondas have BARO or PA sensors to measure the outside air pressure that tinkerbell mentioned above for high altitudes

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yeah, they do, but not in Australia (it is too flat here).

however, that is not what my erroneous “compares” statement was alluding to...

my mistake was trying to convey the ‘absolute’ nature of the “thing” that the MAP sensor represents, it being an ‘absolute’ measurement and not real representation of vacuum i.e. it takes the vacuum represents it as a pressure

but it was early, i had just arrived at work and it seemed like pornstar needed some technical input to fuel his attempt to lead us to the controversial conclusion that MAP sensors are really just very very basic temperature sensors, for whatever bizarre reason he wanted to do that…

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Originally Posted by tinkerbell

yeah, they do, but not in Australia (it is too flat here).

however, that is not what my erroneous “compares” statement was alluding to...

my mistake was trying to convey the ‘absolute’ nature of the “thing” that the MAP sensor represents, it being an ‘absolute’ measurement and not real representation of vacuum i.e. it takes the vacuum represents it as a pressure

but it was early, i had just arrived at work and it seemed like pornstar needed some technical input to fuel his attempt to lead us to the controversial conclusion that MAP sensors are really just very very basic temperature sensors, for whatever bizarre reason he wanted to do that…

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AUDM 1989 A20A4 Accord had a baro under the glove box, all POA ECU for 94-98 have in the ECU, A20A4 prelude just like the accord under the glove box. OBDII P30 have the BARO in the ECU. 94 ledgend ECU has it as well. these are jsut the ones Iv seen Im sure there are more in other models :)

I know for a fact that the BARO sensor is used in the code as a backup to the MAP sensor when there is a problem with the MAP sensor.

I dont actually know what the BARO does, exactly, however it must function similar to the MAP based purely from what ive seen in the code.

well, it is funny you should say that you dont know what it does - considering you have seen the raw code from the ECU's

if in fact ECU-MAN is correct (i dont see why he wouldnt be, i simply had heard Honda decided not to use BARO sensors in Aust. due to lack of any mountains) and Aussie Hondas do have the BARO sensor then the ECU's do actually *compare* the outside air to the MAP signal and use this as an altitude correction function in determining injector PW's...

so for your info - the BARO does not function as a back up to the MAP sensor - how could it? it is not even connected to the intake manifold...

and it is exactly the same as the MAP sensor in its reference voltages as it is the same type of sensor.

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Originally Posted by ProECU

its an absolute sensor because it is relative to atmosphetic pressure

ie, stock MAP sensor reads 1000mbar = 1Bar is still not boost.
anything over this is boost. That because the first 1000mbar is atmosphetic.

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so is it possible for a N/A car to produce over 1bar? (boost).

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Originally Posted by fueltank

so is it possible for a N/A car to produce over 1bar? (boost).

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yes, through a carefully designed intake and only when the car is moving (probably rapidly)...

it is much easier to do this for motorbikes, these commonly have Ram-air induction...

hmmm i never thought about it like that dave.

to be honest i dont see how it could create a pressure greater than 100kpa because there is no other force besides the atmo pressure creating the induction into the engine.

but im not saying its not impossible. wanna explain how it becomes greater than atmo pressure without another force exerting compaction or compression?

Tinkerbell
I find it interesting how you can comment with such confidence as to the operation of the BARO sensor when you have no clue what a MAP sensor is.

NO offence intended here, but, Get a clue my friend, you contradict yourself above when you mention the BARO & MAP share the same reference voltages. Why would they share same voltages but have different operation.

Stop posting false information to the masses if you clearly do not know for certain.

For those who are interetsted, here is a segment of the code detailing the MAP & BARO definitions
F5 A4 : LB A, A4 ; Load Baro (as Backup MAP)
EA 12 05 : JBS off 12.2, 0A15 ; jmp if MAP error
EC 12 02 : JBS off 12.4, 0A15 ; jmp if MAP error
F5 A7 : LB A, A7
8A : STB A, R2
60 00 70 : MOV X1, #7000 ; MAP constants

FACT: some Australian delivered cars DO have BARO sensors. Ive seen them in OBD2
FACT: BARO is a backup for the MAP sensor
FACT: NA cars can see boost ONLY when volumetric efficiency is greater than 100%

This is my evidence to support my claim, where is yours?

Regards
ProECU

taken from tech2tech.net:

All Rights Reserved 2000 Sure Seal Products Inc
This manual printed 4/9/00 from the file pgmfiobd_002.
14 MAP / BARO Sensors
14.1 General Overview
The manifold absolute pressure (MAP) sensor and the barometric pressure (BARO) sensor are virtually identical sensors. One reports intake manifold pressure information to the engine control module (ECM) and one reports atmospheric pressure information to the ECM. They both use the same pressure-sensing component and therefore will indicate the same voltage when both are measuring the same pressure, such as key on/engine off (KOEO).
Both these sensors report the values in absolute pressure to a scan tool. Absolute pressure is just another way to measure vacuum. Absolute pressure uses a total vacuum as its base and therefore our normal environment is considered a pressure.
The pressure unit is in inches of mercury (HG) just like vacuum. The result is that the absolute pressure readings are similar to vacuum readings except the values are opposite. A high absolute pressure reading means a lower vacuum.

Now that you are totally confused, let me make a suggestion. Forget vacuum readings and absolute pressure readings and just use the input voltages to monitor the engine vacuum. You can see from the table that the MAP input voltage at idle,
no load, should be .95 volts. Remember that number, it is one of the critical numbers that you will need to memorize. If the MAP voltage is just under 1 volt at
idle, with no load, the engine vacuum is right. So, why not just use a vacuum gauge? A digital volt-ohm meter (DVOM) hooked onto the MAP or BARO sensor input wire is the most accurate way to measure the engine vacuum. Most vacuum gauges are not very accurate and the input voltage is the signal that the ECM monitors. Regardless of what your vacuum gauge reads you will need to check the
sensor by checking the input voltage anyway.
When a Honda is running extremely rich or lean, always check the MAP sensor input voltage first. Chapter 7 is dedicated to the MAP sensor / injector PW relationship.

14.2 How Do They Work?
The MAP/BARO sensors are standard 5-volt reference sensors. The ECM applies approximately 5.0 volts and a ground to the sensor on two wires and a third wire returns to the ECM an input voltage, as shown in Illustration 14-1.
The normal MAP input voltage is approx. .9 volt at idle, with no load. At wide-open throttle under a load or KOEO the voltage should be close to 2.75 volts or the same as the BARO sensor voltage. The normal BARO input voltage is approximately 2.75 volts. This will vary slightly depending on your elevation and the atmosphere's barometric pressure.