Air Density Compensation Table

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Sep 29, 2008, 09:12 PM

mrfred

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Air Density Compensation Table

Just posting some info on the air density compensation table that is used to calc airflow rate and temp/density compensated load. Here is the ECUFlash definition for the 88590015 ROM:

Code:

<scaling name="AirDensComp" units="Air Density Correction" toexpr="x/129" frexpr="x/129" format="%.3f" min="0" max="2" inc="0.01" storagetype="uint8" endian="big"/>
<table name="Air Density Compensation" category="Misc" address="30fe" type="2D" level="2" scaling="AirDensComp">
  <table name="MAF Air Temp" address="714a" type="Y Axis" elements="8" scaling="Temp"/>
</table>

The table values and a plot of the values are shown below. A curve fit to the data in the plot shows that the density compensation follows a 1/T correlation indicating that the compensation values follow the ideal gas law (PV=nkT). The fact that it follows the ideal gas law means that this table is not what I could consider to be an "adjustable" table. Instead, its a baseline compensation, and I believe that there are other tables used to tweak the air density compensation for fuel control.

Here are the table values:

Here a plot of the values showing a 1/T relationship between the compensation value and air temperature:

Attached Thumbnails

Air Density Compensation Table-air-density-comp-graph.gif

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Last edited by mrfred; Sep 29, 2008 at 09:16 PM.

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Sep 29, 2008, 09:36 PM

cpoku

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you are a fricken genius...

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Sep 30, 2008, 08:46 AM

dudical26

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what are the implications or further uses of this information?

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Sep 30, 2008, 09:32 AM

mrfred

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Quote:

Originally Posted by dudical26

what are the implications or further uses of this information?

Just trying to get across the need to leave this table alone. I could have just not posted anything, but eventually someone will post this table, so I figured it would be better to post the correct information first.

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Sep 30, 2008, 09:40 AM

l2r99gst

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For 96940011:

Code:

<scaling name="AirDensComp" units="Air Density Correction" toexpr="x/129" frexpr="x/129" format="%.3f" min="0" max="2" inc="0.01" storagetype="uint8" endian="big"/>
	<table name="Air Density Compensation" category="Misc" address="2dc2" type="2D" level="2" scaling="AirDensComp">
  		<table name="MAF Air Temp" address="5ec8" type="Y Axis" elements="8" scaling="Temp"/>
	</table>

As MrFred stated, it's just a table that the ROM uses for a lookup for a PV=nRT calculation. There are few lookup tables similar to this that I remember mrfred coming across before. You should never have to change it, since it's basically just a lookup for a calculation.

Last edited by l2r99gst; Sep 30, 2008 at 09:42 AM.