mean91

Guys,

I am tuning a 436 stroker with a big cam 254@.050, and AFR 220 heads with an 8D ecm. I am trying to obtain a better understanding of the Baro tables in Tunercat. There are two tables that are exposed by the software, Volumetric Efficiency Multiplier Vs. Baro, and Barometric Pressure Offset (Kpa) Vs. RPM Vs. TPS. I think that I understand the first table, please correct me if I am way off. I believe that the first table is used to compensate for Kpa limit changes, for example when driving at higher altitudes. At a higher altitude, the total Kpa will be less, so the table increases the VE with a multiplier. Again, please let me know if this is correct or not. The second table, (Barometric pressure offset), I really don't have a clue, nor do I know what to set the values to. I have changed the values up and down and have not noticed a difference. Anyone with some info on these tables, please post.

RBob

iTrader: (1)

It is always helpful to post the addresses of the tables. The names used vary across the board. However, as a guess, the Volumetric Efficiency Multiplier Vs. Baro table is used to compensate for the increased efficiency of the exhaust as the barometric pressure drops.

Such as at higher elevations, the VE increases due to the lower back pressure on the exhaust.

The Barometric Pressure Offset (Kpa) Vs. RPM Vs. TPS is likely for the pseudo barometric pressure read. The ECM regularly uses the MAP, TPS, and RPM to calculate a new barometric pressure value. This value is sometimes further adjusted whether the A/C is on and sometimes using the current IAC position.

RBob.

mean91

I am posting the guts of the tables from my copy of the ECM hack. Hopefully this helps others identify what I am trying to figure out.

This is the first table I mentioned
;--------------------------------------------------
; VE Mult vs BARO
;
; TBL = MULT * 128
;--------------------------------------------------
; MULT Kpa BARO
;----------------------------------
L881F: FCB 152 ; 1.188 65
FCB 146 ; 1.141 75
FCB 139 ; 1.086 85
FCB 133 ; 1.039 95
FCB 128 ; 1.000 105
;--------------------------------------------------


This is the data for the second table (Tunercat shows it all in one table)
***************************************************
* BARO FORM PARAM'S
*
***************************************************
L86C3: FCB 96 ; MIN TPS FOR BARO UPDATR, 37.5 %
; ARG = VAL * 2.56
;
L86C4: FCB 1 ; MAX DIFF MAP FOR BARO UPDATE 0.31 Kpa
; ARG = VAL * (256/80)
;
L86C5: FCB 144 ; READ BARO THERSH 3600 RPM
; ARG = VAL/25
;
L86C6: FCB 11 ; MAX BARO OFFSET THRESH, 4 Kpa
; ARGD= VAL * 2.71
;--------------------------------------
; BARO PRESS vs RPM & TPS
;.; ORG $86C7
;
; Table = Kpa * 2.71
;--------------------------------------
L86C7:
FCB 16 ; RPM min,
FCB 48 ; TPS min
FCB 6 ; Num line in table
;--------------------------------------
; 1200 RPM Kpa TPS
;--------------------------------------
FCB 8 ; 2.952 37.5%
FCB 3 ; 1.107 50.0
FCB 1 ; 0.369 62.5
FCB 0 ; 0 75.0
FCB 0 ; 0 87.5
FCB 0 ; 0 100.0
;--------------------------------------
; 2400 RPM Kpa TPS
;--------------------------------------
FCB 16 ; 5.904 37.5%
FCB 16 ; 5.904 50.0
FCB 8 ; 2.952 62.5
FCB 5 ; 1.845 75.0
FCB 3 ; 1.107 87.5
FCB 1 ; 0.369 100
;--------------------------------------
; 3600 RPM Kpa TPS
;--------------------------------------
FCB 16 ; 5.904 37.5%
FCB 16 ; 5.904 50.0
FCB 16 ; 5.904 62.5
FCB 16 ; 5.904 75.0
FCB 11 ; 4.059 87.5
FCB 5 ; 1.845 100
;--------------------------------------

mean91

Below is how Tunercat displays these tables.

Volumetric Efficiency Multiplier Vs. Baro
Kpa Mult.
65 1.016
75 1.008
85 1.000
95 1.000
105 1.000


Barometric Pressure Offset (Kpa) Vs. RPM Vs. TPS
TPS RPM
1200 2400 3600
37.5 3.0 5.5 5.9
50 1.1 5.5 5.9
62.5 0.4 3.0 5.9
75.0 0.0 1.8 5.9
87.5 0.0 1.1 4.1
100 0.0 0.4 1.8

84Elky

I’ll take a shot at answering your questions.

Quote:

Originally Posted by mean91

I think that I understand the first table, please correct me if I am way off. I believe that the first table is used to compensate for Kpa limit changes, for example when driving at higher altitudes. At a higher altitude, the total Kpa will be less, so the table increases the VE with a multiplier. Again, please let me know if this is correct or not.

This is the table at 0x881F and appears to do exactly what you indicated – increases VE to compensate for decreases in BARO pressure. This adjustment is always made every pass through the Fuel Minor Loop (every 12.5ms) without any restrictions as to RPM, kPa, TPS%, etc.

Quote:

The second table, (Barometric pressure offset), I really don't have a clue, nor do I know what to set the values to. I have changed the values up and down and have not noticed a difference.

This is the table at 0x86C7. The value extracted from this table based on RPM and TPS% is added to Current MAP to create a new BARO kPa. The BARO kPa is used elsewhere in the code to make pressure related decisions. This BARO kPa update is considered every 100ms, but will only occur if certain very restrictive conditions are met:

• TPS% change in the past 12.5ms must have increased <= 1.17%; a decrease is not considered a change
• TPS% must be > 37.5%
• RPM must be < 3600

Because the restrictive conditions necessary for the BARO recalculation, and even if recalculation occurs, the small additive value is likely why you don’t see any effect when changing the values in this table.

Hope this helps.

mean91

84Elky,
Thank you for helping me out with the functional designs of these two tables.