MAP Sensors

[ECU-MAN]

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

[ProECU]

The MAP pressure sensor has the same operation throughout the rev range in that its a sensor which measures pressure and "Vacuum" to some extent SO in terms of High revving NA, it is as important as low revving NA.

The job of the map sensor is to tell teh ECU how much fuel/ignition is required at a particular MAP vs RPM setting. How do i know this, well ive decompiled the bin file (ala hondata) and read the code.

The MAP sensor does NOT compare the outside pressure AT ALL. It has certain boundaries, a min/max value as a check for sensor validity. If the voltage exceeds these tolerances, a code (CEL) is returned.

tinkerbell is incorrect by stating that vacuum determines power, this is NOT the case. The ECU will only see vacuum from the MAP sensor under idling, or when you back off the gas pedal.
Power is determined by the quality of the burn in the combustion chamber (a/f) and the ignition (adv/ret) combined with many other factors such as engine load, fuel quality etc.

Cylinder filling on the other hand, is a product of piston velocity and also a process commonly known as scavenging. This is the process by which cam overlap causes a low pressure condition in the cylinder head, hence mixture is drawn from high pressure to low pressure, increasing the amount of fuel at any given combustion process.

Manifold pressure is not directly related to the combustion process. Take for example a forced induced application.
You have probably heard people talking about B16's as being a torquless motor, this is due to the low piston speeds (long rods) at low rpm.

On the other hand, the D-series motors have more torque and are "nicer" to drive at low rpm's (smaller rod -> faster piston speeds)

This is somewhat of a side-track, but hopefully an insightful one.

ProEcu

[pornstar]

thats an excellent explanation proECU. The map sensor is a common tricky sensor many get confused by. From what i have laernt, it is even less complicated than that, it merely is a temperature sensor in very very basic terms!

[tinkerbell]

so why is it called a Manifold Absolute Pressure sensor?

[pornstar]

because if u think about what the amount of pressure in the manifold is, the air is a particular volume but that volume is not the only factor, desnity si the factor to consider.

density is a function of heat thats what i said about the sensor in VERY VERY VERY BASIC terms is

[tinkerbell]

edited post.

[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.

[wynode]

Great info ProECU

[pornstar]

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

[tinkerbell]

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

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…

[ECU-MAN]

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…

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

[ProECU]

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.