Inverse MAT array (F31M) in $58
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Engine: GM 2.0XE
Inverse MAT array (F31M) in $58
Anybody know why the standard contents of this array in the Sunbird calibration stop changing above 23.5 C ?
The ideal gas law indicates that the air temperature can have a significant effect on air mass above that temperature so, unless the array is changed or there's compensation in the code that I haven't found yet, then the A/F mixture is going to get richer above 23.5 C - when desired A/F is constant.
Apologies if this is old hat. I've searched and haven't found an explanation.
The ideal gas law indicates that the air temperature can have a significant effect on air mass above that temperature so, unless the array is changed or there's compensation in the code that I haven't found yet, then the A/F mixture is going to get richer above 23.5 C - when desired A/F is constant.
Apologies if this is old hat. I've searched and haven't found an explanation.
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Re: Inverse MAT array (F31M) in $58
Don't know whether anybody's interested :-) but I have now perfectly matched every factor in $58's steady state (meaning: no acceleration enrichment or deceleration enleanment or closed loop or any other special
contributions) injector base pulse width calculation with its equivalent derived directly from the ideal gas law. It is now absolutely clear that the standard Sunbird inverse MAT/IAT look-up array (F31M) has been 'adjusted' from theoretically correct, for whatever reasons.
This plot: http://213.162.107.39/temp/GM_invers...tor_vs_IAT.gif shows the only contribution that the MAT/IAT makes to the steady state BPW calculation. The contribution is made via a multiplying factor in the range 0 to 1.
The magenta line is the multiplying factor arising from the values that GM
put in the inverse MAT/IAT look-up array (F31M) for the Sunbird. The dark
blue line is the theoretically correct multplying factor.
The GM contribution stops changing at 23.5C but only matches the theoretical line at 50 C. So I'm now wondering why GM would make it such that the mixture was lean below 50 C and rich above it...
Just out of curiosity, does anybody know if 50 C the normal running air temperature for the Sunbird or Sy/Ty?
I'd also be interested to hear if other GM codes use an inverse MAT/IAT look-up array, and what's in there. From what I can see of $8D, the division is performed in the code.
contributions) injector base pulse width calculation with its equivalent derived directly from the ideal gas law. It is now absolutely clear that the standard Sunbird inverse MAT/IAT look-up array (F31M) has been 'adjusted' from theoretically correct, for whatever reasons.
This plot: http://213.162.107.39/temp/GM_invers...tor_vs_IAT.gif shows the only contribution that the MAT/IAT makes to the steady state BPW calculation. The contribution is made via a multiplying factor in the range 0 to 1.
The magenta line is the multiplying factor arising from the values that GM
put in the inverse MAT/IAT look-up array (F31M) for the Sunbird. The dark
blue line is the theoretically correct multplying factor.
The GM contribution stops changing at 23.5C but only matches the theoretical line at 50 C. So I'm now wondering why GM would make it such that the mixture was lean below 50 C and rich above it...
Just out of curiosity, does anybody know if 50 C the normal running air temperature for the Sunbird or Sy/Ty?
I'd also be interested to hear if other GM codes use an inverse MAT/IAT look-up array, and what's in there. From what I can see of $8D, the division is performed in the code.
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Re: Inverse MAT array (F31M) in $58
Hard to say why the tune is set up as such. Being that it is a turbo'd engine will affect the intake charge temperature. Going rich may be GM's way of protecting the engine from melting. If I had to guess, that would be my guess. IIRC on the Sunbirds the intake charge temperature sensor is in the intake manifold.
Many other Mask's use an inverse IAT/MAT term for the PW calculation. In particular the $88 ('7730 code) uses this table:
The BPC is multiplied by the value in the table and divided by 256.
There is another table that defines the blend of CTS & IAT according to airflow. Note that in this setup the intake charge temperature sensor is in the air cleaner, which is divorced from the engine. And no intake heating other then the throttle body water.
RBob.
Many other Mask's use an inverse IAT/MAT term for the PW calculation. In particular the $88 ('7730 code) uses this table:
Code:
; --------------------------------------
;
; Inverse Coolant term vs. IAT/CTS value
;
; Used for PW calculation
;
; stored in L00A1
; --------------------------------------
;-----------------------------
; ; val ; °C
;-----------------------------
L88A1 FCB 216 ; -40
FCB 204 ; -28
FCB 195 ; -16
FCB 186 ; -4
FCB 178 ; 8
FCB 171 ; 20
FCB 164 ; 32
FCB 158 ; 44
FCB 152 ; 56
FCB 148 ; 68
FCB 145 ; 80
FCB 141 ; 92
FCB 138 ; 104
FCB 134 ; 116
FCB 131 ; 128
FCB 129 ; 140
FCB 127 ; 152 There is another table that defines the blend of CTS & IAT according to airflow. Note that in this setup the intake charge temperature sensor is in the air cleaner, which is divorced from the engine. And no intake heating other then the throttle body water.
Code:
; --------------------------------------
;
; Filter coef's for IAT value into coolant value
;
; Blends IAT into CTS to create a IAT/CTS value
;
; --------------------------------------
;-----------------------------
; ; coef ; gms/sec
;-----------------------------
L8A07 FCB 180 ; 0
FCB 186 ; 16
FCB 190 ; 32
FCB 195 ; 48
FCB 198 ; 64
FCB 202 ; 80
FCB 205 ; 96
FCB 209 ; 112
FCB 214 ; 128
FCB 217 ; 144
FCB 221 ; 160
FCB 225 ; 176
FCB 228 ; 192
FCB 231 ; 208
FCB 234 ; 224
FCB 236 ; 240
FCB 243 ; 256 Thread Starter
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Re: Inverse MAT array (F31M) in $58
Thanks, that's very helpful.
It sounds like $88 and $58 are similar. In $58 the MAT/IAT contribution is in the range 0 to 255 and is divided by 256 and multiplied by the running BPW total. The inverse MAT/IAT array is scaled as 50,000/temp(Kelvin).
From -40 to +56 C, your first $88 array matches extremely well with 50,000/temp(Kelvin) (i.e. no corrections to the ideal gas law). Above +56 C, however, it generates an increasingly higher BPW factor, so making the mixture theoretically a bit rich - but not by much. These are the kind of values that I was expecting to see in $58 - but I guess the Turbo application makes it weird.
I see from Ludis' site that $88 ran on a N/A engine - which is what my application is. I've now set the $58 inverse MAT/IAT array entirely to 50,000/temp(Kelvin) as a starting point for tuning. My air temperature sensor is a thermistor sited in the engine bay near the air filters - so equivalent to the IAT of $88 rather than the MAT of $58. If I ever see temperatures above +56 C, I think I'll modify the values like the $88 array.
Thanks again.
It sounds like $88 and $58 are similar. In $58 the MAT/IAT contribution is in the range 0 to 255 and is divided by 256 and multiplied by the running BPW total. The inverse MAT/IAT array is scaled as 50,000/temp(Kelvin).
From -40 to +56 C, your first $88 array matches extremely well with 50,000/temp(Kelvin) (i.e. no corrections to the ideal gas law). Above +56 C, however, it generates an increasingly higher BPW factor, so making the mixture theoretically a bit rich - but not by much. These are the kind of values that I was expecting to see in $58 - but I guess the Turbo application makes it weird.
I see from Ludis' site that $88 ran on a N/A engine - which is what my application is. I've now set the $58 inverse MAT/IAT array entirely to 50,000/temp(Kelvin) as a starting point for tuning. My air temperature sensor is a thermistor sited in the engine bay near the air filters - so equivalent to the IAT of $88 rather than the MAT of $58. If I ever see temperatures above +56 C, I think I'll modify the values like the $88 array.
Thanks again.
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Re: Inverse MAT array (F31M) in $58
Can you post the values you put into the table? I am curious what you have in there. Also any idea of what the formula would be for that table in $58 to display the values. None of the hacs I have found have one listed for it.
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Re: Inverse MAT array (F31M) in $58
As stated above, the formula I used is: 50,000/temp(Kelvin). This fits in perfectly with the rest of the ideal gas law calculation in $58,
I've put the following (decimal) values in:
106 (50,000/106 ~ 471 Kelvin = 198 C)
123
131
137
142
145
149
152
155
158
161
165
169
173
179
189
214 (50,000/214 ~ 233 Kelvin = -39 C)
This gives inverse temp as constant/temp with no 'safety' correction factors e.g. to make the mixture deliberately rich at higher temps - as the $88 code has. Hence the above values could cause harm (at user's risk). They are probably highly unsuitable for a turbo application.
I've put the following (decimal) values in:
106 (50,000/106 ~ 471 Kelvin = 198 C)
123
131
137
142
145
149
152
155
158
161
165
169
173
179
189
214 (50,000/214 ~ 233 Kelvin = -39 C)
This gives inverse temp as constant/temp with no 'safety' correction factors e.g. to make the mixture deliberately rich at higher temps - as the $88 code has. Hence the above values could cause harm (at user's risk). They are probably highly unsuitable for a turbo application.
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