Intakes, Fuel Trims, and AFR
Slightly off topic, but for everyone who's not an expert in the area: I was studying up on how fuel trims work earlier this week and found a page that had lots of very good info that might help some of those following this thread. enjoy 
It does not...It just carries over from closed loop cruise into WOT operation. So even though the LTFT cruise is not adding/subtracting fuel at WOT, it adds/aubtracts the fuel it has calculated in closed loop to WOT. So if LTFT cruise is X, then the AFR becomes, target AFR+X. X stays the same in WOT operation as it was during closed loop cruise. It is simply added to the target AFR.
the 3 fuel trims (Low, Medium and High - forget STFT for a sec) are MAF-Hz bins, so Low MAF-Hz, Med MAF-Hz and High MAF-Hz... High MAF Hz means open loop - which also means you probably not going to run stoich, you might run ~11:1 AFR... which means the 02 sensors will be useless and thus cant give you a reading on how far lean or rich you are from stoich...
oh you need the XML to go in evo10base.xml:
Code:
<table name="MAF Scaling Part 1" category="Fuel" type="2D" level="2" scaling="uint16">
<table name="Volts" type="Y Axis" elements="44" scaling="VoltsADC1023"/>
</table>
<table name="MAF Scaling Part 2" category="Fuel" type="2D" level="2" scaling="uint16">
<table name="Volts" type="Y Axis" elements="44" scaling="VoltsADC1023"/>
</table>
<table name="MAF Scaling Part 3" category="Fuel" type="2D" level="2" scaling="uint16">
<table name="Volts" type="Y Axis" elements="42" scaling="VoltsADC1023"/>
</table>
oh you need the XML to go in evo10base.xml:
Code:
<table name="MAF Scaling Part 1" category="Fuel" type="2D" level="2" scaling="uint16">
<table name="Volts" type="Y Axis" elements="44" scaling="VoltsADC1023"/>
</table>
<table name="MAF Scaling Part 2" category="Fuel" type="2D" level="2" scaling="uint16">
<table name="Volts" type="Y Axis" elements="44" scaling="VoltsADC1023"/>
</table>
<table name="MAF Scaling Part 3" category="Fuel" type="2D" level="2" scaling="uint16">
<table name="Volts" type="Y Axis" elements="42" scaling="VoltsADC1023"/>
</table>
Scaling:
Code:
<scaling name="VoltsADC1023" units="Volts" toexpr="x*5/1023" frexpr="x*1023/5" format="%.2f" min="0" max="16" inc="0.05" storagetype="uint16" endian="big"/>
I've been logging my fuel trims on the stock intake with 800cc injectors and my trims are -12.xx at idle and -11.xx during cruise. Would this explain why on my Hi-oct fuel map I can adjust my tables to about 12.5-12.7 in the correct load cells but only register low 11 afr's on the wideband?
When installing new injectors you SHOULD ALWAYS setup the scaling+latencies so that your trims are as close to 0% as possible.
Once your injectors are tuned properly you can then begin tuning your fuelmap...
Once your injectors are tuned properly you can then begin tuning your fuelmap...
Hmm... I had slightly different addresses for MAF Scaling from Gunzo. I wonder if that is why I'd been having so much trouble with trying to compensate for an intake. Maybe I'll try these ones and see if it improves anything.
Here's what I had (For 52680015):
The first one is the same, but the others differ.
Here's what I had (For 52680015):
Code:
<table name="MAF Compensation" address="5753a"> <table name="X" address="615ea"/> </table> <table name="MAF Compensation #2" address="5758a"> <table name="X" address="6163a"/> </table> <table name="MAF Compensation #3" address="575da"> <table name="X" address="6168a"/> </table>
Though I lined up the data from the tables I used with the single table from one of the Cobb AP maps, and the axis matched up. I was comparing what Cobb used for MAF Scaling on an AEM Intake with stock since I don't have my stock intake to do the scaling myself.
Code:
<scaling name="MAFVoltScaling" units="units" toexpr="x*5/1024" frexpr="x*1024/5" format="%.3f" min="0" max="5" inc="1" storagetype="uint16" endian="big"/> <table name="MAF Compensation" category="Fuel" type="2D" scaling="AirFlow16"> <table name="X" type="X Axis" elements="40" scaling="MAFVoltScaling"/> </table> <table name="MAF Compensation #2" category="Fuel" type="2D" level="1" scaling="AirFlow16"> <table name="X" type="X Axis" elements="40" scaling="MAFVoltScaling"/> </table> <table name="MAF Compensation #3" category="Fuel" type="2D" level="1" scaling="AirFlow16"> <table name="X" type="X Axis" elements="50" scaling="MAFVoltScaling"/> </table>
This could be why I was getting crazy boost/load curves when I tried MAF Scaling! If only the first table was correct, it would reach the second table and think there was a drop in airflow. That might explain why I was getting a "double peaking" load curve. Sweet.
Last edited by xPRimNT; Aug 3, 2009 at 09:06 AM.
Evolving Member
Joined: Oct 2008
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From: Ukraine
Aggressive mivec lean AFR by 1-1.5 afr at hight load. So changing mivec on low load will affect on Fuel Trims? So we should recalibrate low load AFR before tuning hight load AFR?
I'm running stock intake (except Upper IC pipe) with pretty aggressive mivec . My FuelTrim_Cruise is -4.5% and FuelTrim_Idle
jumping between -4 and -3.2.
I'm running stock intake (except Upper IC pipe) with pretty aggressive mivec . My FuelTrim_Cruise is -4.5% and FuelTrim_Idle
jumping between -4 and -3.2.