MAP values
02-01-2008, 05:23 PM
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MAP values
Hey guys...I might be overthinking this, or I might not.
Talking about comparing MAP values from key on, engine off to MAP values at WOT max rpm with respect to pressure and density altitude.
Pressure altitude is easy, just how high you are above MSL according to ambient pressure without respect to temp.
Since density altitude is pressure altitude corrected for non-standard temps, does the MAP sensor give density altitude in Kpa?
e.g.
sea level, standard conditions, MAP should be 100 Kpa. now, we take it up to max RPM and the MAP was 100 KPA. Now raise the ambient temp to 100 deg F. Will the KOEO value still be 100 kpa? I wouldn't think so, since the hotter air temps thin the air out, giving a lower KOEO Kpa and therefore a lower WOT Kpa.
How would an IAT/MAT sensor affect things in terms of Kpa values displayed?
just kinda bored thinking about things.
Let's say I go out to my truck when it's 20 degrees F ambient and MAP Kpa is 84. Now, it warms up to 70 deg F and MAP Kpa is now 82.
key on, engine off both times.
I think that's the way it works. The increased temp thinned the air out. THe MAP sensor is oblivious to temp, all it knows is what is present, right?
I guess I'm kinda wondering how the BARO function in the computer works, also.
sorry if I confused anyone!!!
Talking about comparing MAP values from key on, engine off to MAP values at WOT max rpm with respect to pressure and density altitude.
Pressure altitude is easy, just how high you are above MSL according to ambient pressure without respect to temp.
Since density altitude is pressure altitude corrected for non-standard temps, does the MAP sensor give density altitude in Kpa?
e.g.
sea level, standard conditions, MAP should be 100 Kpa. now, we take it up to max RPM and the MAP was 100 KPA. Now raise the ambient temp to 100 deg F. Will the KOEO value still be 100 kpa? I wouldn't think so, since the hotter air temps thin the air out, giving a lower KOEO Kpa and therefore a lower WOT Kpa.
How would an IAT/MAT sensor affect things in terms of Kpa values displayed?
just kinda bored thinking about things.
Let's say I go out to my truck when it's 20 degrees F ambient and MAP Kpa is 84. Now, it warms up to 70 deg F and MAP Kpa is now 82.
key on, engine off both times.
I think that's the way it works. The increased temp thinned the air out. THe MAP sensor is oblivious to temp, all it knows is what is present, right?
I guess I'm kinda wondering how the BARO function in the computer works, also.
sorry if I confused anyone!!!
02-02-2008, 12:14 PM
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Car: check
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Transmission: check
Re: MAP values
The MAP only reads presssure. If the ambient pressure changes due to a temperature change, the MAP will read the different pressure. However, a change in ambient temperature doesn't always relate to a change in ambient pressure.
As you posted density altitude takes into account barometric pressure, temperature, and humidity. The baro pressure is read by the MAP sensor, and the temperature by the IAT sensor. Humidity is left out.
The ECM reads the MAP sensor early on in the key-on init routine. That value is kept as the barometric pressure. Then as the vehicle is driven the ECM does pseudo baro reads. In this case there are qualifiers: steady TPS, TPS > threshold, RPM < threshold. IOW: lots of throttle at low(er) RPM.
The MAP value is used along with a tweak for TPS% and a tweak for RPM, and out comes a pseudo barometric pressure value. Which is slowly blended with the current baro value. This is to have a slow adjustment to the ECM's baro reading.
RBob.
As you posted density altitude takes into account barometric pressure, temperature, and humidity. The baro pressure is read by the MAP sensor, and the temperature by the IAT sensor. Humidity is left out.
The ECM reads the MAP sensor early on in the key-on init routine. That value is kept as the barometric pressure. Then as the vehicle is driven the ECM does pseudo baro reads. In this case there are qualifiers: steady TPS, TPS > threshold, RPM < threshold. IOW: lots of throttle at low(er) RPM.
The MAP value is used along with a tweak for TPS% and a tweak for RPM, and out comes a pseudo barometric pressure value. Which is slowly blended with the current baro value. This is to have a slow adjustment to the ECM's baro reading.
RBob.
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