calibrating the map sensor

[Seight-v8]

hello all,

trying to make sense of my map sensor readings in vemstune.

so todays local weather station says 999mb = 99.9kpa.

So my vemstune reading should be 99kpa....this is atmospheric pressure or 14.5psi

So i presume that the map sensor always reads from atmospheric pressure

So if i was to apply 10psi (69kpa) to the sensor pipe i should in theory have 99+69kpa = 168kpa (24.5psi)

As my pressure gauge says 10psi (69kpa), but in vemstune i am getting 155kpa (22.5psi).

Does this make sense or am i over confusing the matter....

Wanna get this bottomed so i can move on.

cheers for any help

scott

[GintsK]

What sensor you use, and what is current calibration values?

[Seight-v8]

hiya,

I am using the 250kpa version.

i currently have 31.75kpa in the offset, as this is the most vemstune will allow me to enter, and base reading is stll 10kpa away from correct.

i've tried applying 10psi to the pipe but i only get 155kpa.

been thinking for a while theres a problem witht the sensor.

As i am now wanting to drive my car, i want to make sure this is correct.

cheers

scott

[GintsK]

hiya,

I am using the 250kpa version.

i currently have 31.75kpa in the offset,

Something is definitely wrong. 250 range and 10 offset should give close to perfect match!
Is it new board? Onboard sensor? May be you have 300Kpa sensor? Or even 400!

[Seight-v8]

yes, think i will pop the front plate and take a look and see if i can identify it properly.

Sure map sensor info says it should be close to 1.5% accuracy so something is wrong with mine.

cheers

scott

[Seight-v8]

well..

Looks like i have A MPXH6400A map sensor.

I've just disassembled my ecu and found this fitted.....

So i dont have a 250kpa one....but a 400kpa.

Hmmm...gonna put it back together and try the correct setttings & calibration readings again.

cheers

scott

[mattias]

Press F1 for help in the MAP calibration dialog for good starting values for the 'range'. Calibrate the offset according to local atmospheric pressure.

[Seight-v8]

cheers everyone,

Problem solved, changed map sensor to 400kpa and offset to 2kpa in vemstune.

now readings are correct at 99kpa, and 10psi reads 168kpa....

much happier now and moving onwards.

scott

[GintsK]

cheers everyone,

Problem solved, changed map sensor to 400kpa and offset to 2kpa in vemstune.

now readings are correct at 99kpa, and 10psi reads 168kpa....

much happier now and moving onwards.

scott

why you didn't look to topic created by you! 400Kpa and 2kpa offset are also wrong settings:
http://195.159.109.134/vemsuk/forum/index.php/topic,1065.0.html

[GintsK]

Press F1 for help in the MAP calibration dialog for good starting values for the 'range'. Calibrate the offset according to local atmospheric pressure.

I wondering why it is suggested to use actual baro when calibrating offset. This topic is bad example what happens!
In addition for those who lives higher - meteorological barometric pressure is corrected to sea level. So your actual pressure is significant lower.
Also values in help looks little off to me. Look at link above.
Even at 300m altitude your error is 4%!

Gints

[mattias]

GintsK : The range value is what it is, your range calibration is above most peoples knowledge/skill.

The offset on the other hand, I calibrate the offset so that the sensor reads current local pressure. I  use the barometric pressure reading from a local station, you can deduct 1 hPa for each 8 meters above sea level. Where I live the station is just at 8 meters above sea level, so the error is slight. It won't make the car go slower if I miss a decimal..

[GintsK]

GintsK : The range value is what it is, your range calibration is above most peoples knowledge/skill.

sorry, Mattias, I didn't understand you. Or you me.

I mean
1)suggested range values in F1 help is little off  (300KPa sensor)
2) my fixed offsets always gives actual pressure within 1Kpa
3) entering both fixed values would prevent errors like we see in this topic.

Gints

[Denmark]

i think its a problem that the ofset only can be +-32.

that will not make a Subaru oe mapsensor reading right,
i wonder if the offset can be made ,so a bigger number can be put in, so the mapscaling can be made better


/Skassa