Volumetric efficiency

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Oct 12, 2008, 07:24 AM

acamus

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Volumetric efficiency

It seems to me that the MUT_31 logs volumetric efficiency

<DataListItem DataLog="Y" Color="#fa903a" Display="Volumetric Efficiency" LogReference="VE" RequestID="31"
Eval="x/255*100" Unit="%" MetricEval="" MetricUnit="" ResponseBytes="1" GaugeMin="0" GaugeMax="130" ChartMin="0"
ChartMax="130" ScalingFactor="0.01" Notes="Volumetric efficiency is the ratio, how close the actual volumetric flow rate is to the theoretical volumetric flow rate. " Priority="1"
Visible="False" />

Anyone to confirm it on different ROM models?

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Oct 12, 2008, 07:46 AM

l2r99gst

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Is the VE actually being calculated or is this a lookup from a table? Interesting find either way. This would help a lot in many calculations.

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Oct 12, 2008, 08:06 AM

acamus

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My MAP controlled engine has 3 VE tables. But I could not find them in MAF controlled ROMs.
Therefore I assume it is calculated from MAF compensation tables.

Last edited by acamus; Oct 12, 2008 at 08:10 AM.

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Oct 12, 2008, 09:45 PM

acamus

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^ bump,

Anyone to confirm?

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Oct 13, 2008, 02:16 PM

JoeBee

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This variable will be build by a 2D table lookup.
The left row is the same MAF Hz lookup Table that is used by the maf scaling table

Code:

ROM:00005576 MAF_Hz_Tab_row: .data.l RPM_Tab_Find    ; DATA XREF: ROM:off_13B10
ROM:0000557A                 .data.l MAF_Hz_Word
ROM:0000557E                 .data.w h'15
ROM:00005580                 .data.w h'C0
ROM:00005582                 .data.w h'100
ROM:00005584                 .data.w h'200
ROM:00005586                 .data.w h'300
ROM:00005588                 .data.w h'400
ROM:0000558A                 .data.w h'500
ROM:0000558C                 .data.w h'600
ROM:0000558E                 .data.w h'700
ROM:00005590                 .data.w h'800
ROM:00005592                 .data.w h'900
ROM:00005594                 .data.w h'A00
ROM:00005596                 .data.w h'B00
ROM:00005598                 .data.w h'C00
ROM:0000559A                 .data.w h'1000
ROM:0000559C                 .data.w h'1400
ROM:0000559E                 .data.w h'1800
ROM:000055A0                 .data.w h'2000
ROM:000055A2                 .data.w h'2800
ROM:000055A4                 .data.w h'3000
ROM:000055A6                 .data.w h'3800
ROM:000055A8                 .data.w h'4000

The right row is this table. Bez has already called this MAF_Smooth* so I adopt this name. I dont know if this is vol. eff.

Code:

ROM:0000351C MAF_Smooth_Tab: .data.b    2            ; DATA XREF: ROM:off_13B28
ROM:0000351D                 .data.b    0
ROM:0000351E                 .data.l RPM_Tab_Find
ROM:00003522                 .data.b h'80 ; Ç
ROM:00003523                 .data.b h'80 ; Ç
ROM:00003524                 .data.b h'85 ; à
ROM:00003525                 .data.b h'86 ; å
ROM:00003526                 .data.b h'85 ; à
ROM:00003527                 .data.b h'84 ; ä
ROM:00003528                 .data.b h'86 ; å
ROM:00003529                 .data.b h'86 ; å
ROM:0000352A                 .data.b h'86 ; å
ROM:0000352B                 .data.b h'87 ; ç
ROM:0000352C                 .data.b h'87 ; ç
ROM:0000352D                 .data.b h'87 ; ç
ROM:0000352E                 .data.b h'87 ; ç
ROM:0000352F                 .data.b h'89 ; ë
ROM:00003530                 .data.b h'87 ; ç
ROM:00003531                 .data.b h'87 ; ç
ROM:00003532                 .data.b h'85 ; à
ROM:00003533                 .data.b h'85 ; à
ROM:00003534                 .data.b h'85 ; à
ROM:00003535                 .data.b h'85 ; à
ROM:00003536                 .data.b h'85 ; à

This value will be used as a factor in the maf function and build some kind of MAF Airflow value.

Code:

ROM:00013A6E                 mov.l   @(h'E0,pc), r10 ; [00013B50] = BaroTemp_Comp_Value
ROM:00013A70                 mov.w   @r10, r10
ROM:00013A72                 extu.w  r10, r10
ROM:00013A74                 mov.l   @(h'B8,pc), r11 ; [00013B30] = MAF_Smooth_Var
ROM:00013A76                 mov.w   @r11, r11
ROM:00013A78                 extu.w  r11, r11
ROM:00013A7A                 mulu    r10, r11
ROM:00013A7C                 sts     macl, r12
ROM:00013A7E                 mov.l   @(h'A4,pc), r4 ; [00013B24] = MAF_Airflow
ROM:00013A80                 mov.w   @r4, r4
ROM:00013A82                 extu.w  r4, r4          ; r4= MAF_Airflow
ROM:00013A84                 mov     r12, r5         ; r5=r12= MAF_Smooth * BaroTemp_Comp
ROM:00013A86                 mov.w   @(h'3A,pc), r6 ; [00013AC4] = h'4000
ROM:00013A88                 mov.l   @(h'C8,pc), r10 ; [00013B54] = r4_mul_r5_div_r6_round
ROM:00013A8A                 jsr     @r10 ; r4_mul_r5_div_r6_round
ROM:00013A8C                 nop
ROM:00013A8E                 mov.l   @(h'C8,pc), r11 ; [00013B58] = MAF_Airflow_corr_1
ROM:00013A90                 mov.w   r0, @r11

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Oct 13, 2008, 09:24 PM

acamus

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Thanx JoeBee,

I have seen this piece of code in MAF controlled ROMs. The only thing is that I do not have these MAF scalings in my MAP controlled engine, and still have the variable which can be logged via MUT_31 on similar place -> IPW calculation. The only meaning that I can give to what I see in my ROM is Volumetric efficiency, I have logged MUT_31 recently and it takes the values directly from those 3D tables, modifying of these tables has direct effect on IPW. You may call it AirFlow scaling/smoothing in MAF controlled ROM, but there is no measured airflow to scale in MAP controlled one. Barometric reading is scaled at different place.

Last edited by acamus; Oct 13, 2008 at 09:33 PM.

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Oct 13, 2008, 09:44 PM

acamus

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I guess the only way to find out if my assumption is correct is to calculate consumption via VE and compare it with IPW consumption calculation. All necessary variables are already available via MUT

Quote:

MAF Sensor:

MPG = (14.7 * 6.17 * 454 * VSS * 0.621371) / (3600 * MAF / 100)
= 710.7 * VSS / MAF

14.7 - grams of air to 1 gram of gasoline - ideal air/fuel ratio
6.17 - pounds per gallon - density of gasoline
4.54 - grams per pound - conversion
VSS - vehicle speed in kilometers per hour
0.621371 - miles per hour/kilometers per hour - conversion
3600 - seconds per hour - conversion
MAF - mass air flow rate in 100 grams per second
100 - to correct MAF to give grams per second

No MAF (Uses MAP and Absolute Temp to approximate MAF):

IMAP = RPM * MAP / IAT
MAF = (IMAP/120)*(VE/100)*(ED)*(MM)/(R)

MAP - Manifold Absolute Pressure in kPa
IAT - Intake Air Temperature in Kelvin
R - Specific Gas Constant (8.314 JM/K)
MM - Average molecular mass of air (28.97 g/M)
VE - volumetric efficiency measured in percent
ED - Engine Displacement in liters

source:
http://www.mp3car.com/vbulletin/engi...-maf-obd2.html

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Volumetric efficiency

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