P730: Target AFR and how it is used in PE Mode
12-11-2003, 10:20 AM
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P730: BPW and Target AFR, how it is calculated in PE Mode
Admittedly, I am not the best person to be writing this but there seems to be a need for a writeup on how AFR is used in the $8D so I am going to step up to the plate. It would be great if another person who is more proficient at assembly language could review what I have stated and point out errors, etc. In any case, here we go …
In PE Mode the Base Pulse Width (BPW) is calculated from a theoretical Air/Fuel Ratio (AFR). This AFR is independent from the O2 sensor. It is simply a theoretical target value that the ECM is going to make an attempt to achieve without any feedback. When PE Mode is engaged at WOT (according to %TPS Threshold), then both the AUJP and ANHT will start WOT Fuel calculations based off of the stoichiometric value you have set for the constant at L841A (default is the normal 14.7:1 AFR you would expect). This stoichiometric starting value is loaded into memory during the PE routine of the code at LC823 in ANHT and at LC82B in AUJP. The code then modifies this stoichiometric value according to the PE Modifiers (PE %Change to AFR vs. RPM table at L8617 and PE %Change to AFR vs. Coolant table at L860D). This modification is completed according to the following formula:
WOT AFR = 6553.6 / (((TBL L8617 + TBL L860D + 128) * 445) / 256)
TBL L8617 is the decimal value located in the PE %Change to Fuel/Air Ratio vs. RPM table for a specific RPM.
TBL L860D is the decimal value located in the PE %Change to Fuel/Air Ratio vs. Coolant Temp. table for a specific degree C.
This formula is absolutely true to form in the real world using your scanner. The target theoretical AFR is not only stored in memory (at L00F1) for internal calculations, but it is also pushed to the ALDL stream. Anyone who has WOT scans can use the above formula to calculate the target AFR and this target AFR will match the AFR reported via the ALDL. Please keep in mind that this is a theoretical target AFR which is independent of the O2 sensor. Let’s do an example so that you can see how this works. Let’s calculate the AFR for a stock AUJP for 80deg C. and 4000RPMs. The PE for Coolant Temp has a decimal value of 58. The PE for RPM has a decimal value of 148. Please note the use of decimal values and not a calculated percentage! To obtain this decimal value you’ll have to find a way to display the raw hex values in the BIN and then determine it’s decimal equivalent. Using these decimal values our formula above becomes …
WOT AFR = 6553.6 / (((TBL L8617 + TBL L860D + 128) * 445) / 256)
WOT AFR = 6553.6 / (((148 + 58 + 128) * 445) / 256)
WOT AFR = 11.3
I’ve verified this target AFR on my car using Diacom scans from long ago when I was running stock PE tables.
We now have a target theoretical PE AFR value that the ECM stores in memory location L00F1. It is this target AFR that the ECM is going to make an attempt to blindly achieve. However, before proceeding on further calculations the ECM looks to see if it’s current status is Open Loop or Closed Loop. If the ECM is in Closed Loop before going into PE Mode then the ECM will remain in Closed Loop. If the ECM is in Open Loop before going into PE Mode then the ECM will remain in Open Loop. This is important because if the ECM is in Open Loop when engaging PE Mode then the target AFR calculated and stored to L00F1 may or may not be used. If the ECM is in Open Loop then it’s target AFR in almost all cases is a richer AFR than stoichiometric (due to modifying 14.7:1 using the “Open Loop %Change to AFR vs Coolant” table at 845E and the “Open Loop %Change to AFR vs MAP” table at 8420). See code starting at LC82B in ANHT and at LC833 in AUJP where the code compares this Open Loop AFR to the calculated target AFR stored in L00F1. If the Open Loop AFR is less than (i.e. richer than) this calculated target AFR then the Open Loop AFR will be used instead of this calculated AFR by writing it’s value to L00F1. This point is extremely important for those who want consistency on the dyno and at the track since the actual real world AFR as measured by a Wide Band O2 will be different for Closed Loop vs Open Loop if the Open Loop AFR is richer than the Closed Loop PE calculated AFR..
At this point the ECM has a beginning target AFR in L00F1. So, how do we get the actual BPW from this AFR? Follow along …
First thing that is done is that the ECM goes through some initial tests regarding Error 43 (MAP error), Heads Up, and for CCP with Idle Cell Learn. If the MAP sensor is working fine and if the current CCP is greater than the minimum that forces an idle cell learn then the ECM will end up retrieving the stored BLM and BLM Cell information for the current RPM/kPa (load). Yes, this is done even though we are at WOT and in PE Mode. As far as I can tell this is a simple retrieval of information and storage. It is not an update. To view code that actually updates the BLM see the 50ms Air/Fuel minor loop beginning at LCCD8 in ANHT and LCCE0 in AUJP. Under normal conditions this BLM will be stored at L00E0 (see LC9A7 in ANHT and LC9AF in AUJP) to be used later when the BPW is modified using BLMs. However, there is a test done starting at LC9AB in ANHT and at LC9B3 in AUJP which will force a BLM of 128 and store this 128 value in L00E0 in cases where the ECM is in Power Enrichment mode (bit 5 = true for L0046) and if the current BLM is less than 128. What does this mean? In short, it means that lean BLMs (> 128) will be used to modify the BPW at WOT if the ECM is in Closed Loop. The long story is that in a perfect world the VE tables would produce the stoichiometric AFR (again, stoichiometric is the constant at L841A) over all MAP/kPa (this includes the higher kPa columns like the 95 and 100kPa). However, since the world is not perfect (i.e. all cars are different and every single environmental situation can not be accounted for), it is possible that these cells do not produce the stoichiometric AFR. If the ECM knows this via having stored BLM values for those VE cells, then the ECM will implement lean BLM values (> 128) at WOT in order to richen the mixture. This is done in order to ensure that the ECM is starting with a stoichiometric AFR (since, as already pointed out, the ECM needs to start calculations based off of stoichiometric). Of particular note is that GM only implemented lean BLMs (> 128) in PE Mode and not rich BLMs (< 128). The ECM will never subtract fuel at WOT. The argument can be made that GM took precautions to avoid warranty claims in that taking a chance at running rich is less destructive than taking a chance at subtracting fuel at WOT and causing detonation. Moreover, lean conditions always have to be accounted for (if they can be) in order to minimize the chances of detonation and the subsequent consequences thereof.
So, at this point in the discussion we have established that there is a calculated AFR stored in L00F1 and that the ECM has determined the BLM that will be applied to the WOT fuel calculations.
That’s enough for now. I’ll post more later.
Tim
In PE Mode the Base Pulse Width (BPW) is calculated from a theoretical Air/Fuel Ratio (AFR). This AFR is independent from the O2 sensor. It is simply a theoretical target value that the ECM is going to make an attempt to achieve without any feedback. When PE Mode is engaged at WOT (according to %TPS Threshold), then both the AUJP and ANHT will start WOT Fuel calculations based off of the stoichiometric value you have set for the constant at L841A (default is the normal 14.7:1 AFR you would expect). This stoichiometric starting value is loaded into memory during the PE routine of the code at LC823 in ANHT and at LC82B in AUJP. The code then modifies this stoichiometric value according to the PE Modifiers (PE %Change to AFR vs. RPM table at L8617 and PE %Change to AFR vs. Coolant table at L860D). This modification is completed according to the following formula:
WOT AFR = 6553.6 / (((TBL L8617 + TBL L860D + 128) * 445) / 256)
TBL L8617 is the decimal value located in the PE %Change to Fuel/Air Ratio vs. RPM table for a specific RPM.
TBL L860D is the decimal value located in the PE %Change to Fuel/Air Ratio vs. Coolant Temp. table for a specific degree C.
This formula is absolutely true to form in the real world using your scanner. The target theoretical AFR is not only stored in memory (at L00F1) for internal calculations, but it is also pushed to the ALDL stream. Anyone who has WOT scans can use the above formula to calculate the target AFR and this target AFR will match the AFR reported via the ALDL. Please keep in mind that this is a theoretical target AFR which is independent of the O2 sensor. Let’s do an example so that you can see how this works. Let’s calculate the AFR for a stock AUJP for 80deg C. and 4000RPMs. The PE for Coolant Temp has a decimal value of 58. The PE for RPM has a decimal value of 148. Please note the use of decimal values and not a calculated percentage! To obtain this decimal value you’ll have to find a way to display the raw hex values in the BIN and then determine it’s decimal equivalent. Using these decimal values our formula above becomes …
WOT AFR = 6553.6 / (((TBL L8617 + TBL L860D + 128) * 445) / 256)
WOT AFR = 6553.6 / (((148 + 58 + 128) * 445) / 256)
WOT AFR = 11.3
I’ve verified this target AFR on my car using Diacom scans from long ago when I was running stock PE tables.
We now have a target theoretical PE AFR value that the ECM stores in memory location L00F1. It is this target AFR that the ECM is going to make an attempt to blindly achieve. However, before proceeding on further calculations the ECM looks to see if it’s current status is Open Loop or Closed Loop. If the ECM is in Closed Loop before going into PE Mode then the ECM will remain in Closed Loop. If the ECM is in Open Loop before going into PE Mode then the ECM will remain in Open Loop. This is important because if the ECM is in Open Loop when engaging PE Mode then the target AFR calculated and stored to L00F1 may or may not be used. If the ECM is in Open Loop then it’s target AFR in almost all cases is a richer AFR than stoichiometric (due to modifying 14.7:1 using the “Open Loop %Change to AFR vs Coolant” table at 845E and the “Open Loop %Change to AFR vs MAP” table at 8420). See code starting at LC82B in ANHT and at LC833 in AUJP where the code compares this Open Loop AFR to the calculated target AFR stored in L00F1. If the Open Loop AFR is less than (i.e. richer than) this calculated target AFR then the Open Loop AFR will be used instead of this calculated AFR by writing it’s value to L00F1. This point is extremely important for those who want consistency on the dyno and at the track since the actual real world AFR as measured by a Wide Band O2 will be different for Closed Loop vs Open Loop if the Open Loop AFR is richer than the Closed Loop PE calculated AFR..
At this point the ECM has a beginning target AFR in L00F1. So, how do we get the actual BPW from this AFR? Follow along …
First thing that is done is that the ECM goes through some initial tests regarding Error 43 (MAP error), Heads Up, and for CCP with Idle Cell Learn. If the MAP sensor is working fine and if the current CCP is greater than the minimum that forces an idle cell learn then the ECM will end up retrieving the stored BLM and BLM Cell information for the current RPM/kPa (load). Yes, this is done even though we are at WOT and in PE Mode. As far as I can tell this is a simple retrieval of information and storage. It is not an update. To view code that actually updates the BLM see the 50ms Air/Fuel minor loop beginning at LCCD8 in ANHT and LCCE0 in AUJP. Under normal conditions this BLM will be stored at L00E0 (see LC9A7 in ANHT and LC9AF in AUJP) to be used later when the BPW is modified using BLMs. However, there is a test done starting at LC9AB in ANHT and at LC9B3 in AUJP which will force a BLM of 128 and store this 128 value in L00E0 in cases where the ECM is in Power Enrichment mode (bit 5 = true for L0046) and if the current BLM is less than 128. What does this mean? In short, it means that lean BLMs (> 128) will be used to modify the BPW at WOT if the ECM is in Closed Loop. The long story is that in a perfect world the VE tables would produce the stoichiometric AFR (again, stoichiometric is the constant at L841A) over all MAP/kPa (this includes the higher kPa columns like the 95 and 100kPa). However, since the world is not perfect (i.e. all cars are different and every single environmental situation can not be accounted for), it is possible that these cells do not produce the stoichiometric AFR. If the ECM knows this via having stored BLM values for those VE cells, then the ECM will implement lean BLM values (> 128) at WOT in order to richen the mixture. This is done in order to ensure that the ECM is starting with a stoichiometric AFR (since, as already pointed out, the ECM needs to start calculations based off of stoichiometric). Of particular note is that GM only implemented lean BLMs (> 128) in PE Mode and not rich BLMs (< 128). The ECM will never subtract fuel at WOT. The argument can be made that GM took precautions to avoid warranty claims in that taking a chance at running rich is less destructive than taking a chance at subtracting fuel at WOT and causing detonation. Moreover, lean conditions always have to be accounted for (if they can be) in order to minimize the chances of detonation and the subsequent consequences thereof.
So, at this point in the discussion we have established that there is a calculated AFR stored in L00F1 and that the ECM has determined the BLM that will be applied to the WOT fuel calculations.
That’s enough for now. I’ll post more later.
Tim
Last edited by TRAXION; 12-19-2003 at 12:43 PM.
12-11-2003, 02:30 PM
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Beginning where we left off …
At this point in the discussion we have established 2 things:
1) There is a calculated, target, theoretical AFR stored in L00F1 that will be used for determining the BPW.
2) The ECM has determined the BLM that will be applied to the BPW (which will be 128 or higher).
One of the first interesting points to mention before we get to the BPW calculations is that several tests are done starting at LCA2F in ANHT and at LCA37 in AUJP. These tests forward the execution of code to a section which forces an INT of 128. These conditions are…
a) If the ECM is not in Closed Loop
b) If the ECM is in DFCO
c) If the ECM is in Power Enrichment Mode
d) If Highway Mode is enabled.
Since the ECM is in Power Enrichment (given our current conversation) then the INTegrator is forced to 128. This means that no adjustments to BPW will be done based on INT values. The section of code that forces an INT of 128 can be found at LCA85 in ANHT and at LCABD in AUJP. After forcing the INT to 128 the execution of code is forwarded to LCBD9 in ANHT and LCBE1 in AUJP. This means that we end up skipping a whole host of code that is analyzing O2 sensor readings as well as INTegrator update logic. We arrive at a point in the code that retrieves the Volumetric Efficiency (VE) from the VE tables using the current MAP and RPM. An explanation of the routine that retrieves the VE using the current MAP and RPM was explained previously HERE. After retrieving the VE the code then applies the Barometric modifier located in a table at 881F. This is helpful in ensuring correct fueling at different altitudes. Conditional filtering is then applied to this VE as long as ((%TPS > 1.2% and RPM < 1200) and Old Filtered VE value <> New VE). This conditional filtering applies a lag filter routine at LE31C to arrive at a filtered VE based off of the VE calculated after applying the Barometric modifier. The end result is that the current VE is stored in L0067. This is the VE that will be used in calculating the BPW.
We are now at a point in the code where all of the work is done for calculating the BPW. In the ANHT_HAC this is labeled at “CALCULATE SPEED DENSITY” and is located at LCC36. In AUJP it starts at LCC3E. This routine determines the Grams of Air per Cylinder (GMS of Air / CYL) according to the ideal gas law. The ideal gas law states that …
PV=nRT (or rewritten as n = PV/RT)
P = Pressure
V = Volume
n = Number of moles of gas present
R = Universal Gas Constant
T = Temperature
It is easy to see how the ideal gas law can be applied to automobiles since we are trying to determine the moles of air per cylinder which in turn yields the Grams of air per cylinder. The ANHT_HAC yields the following formula…
GMS of Air / CYL = ((MAP - EGR part press) * CYL VOL)/((MAT + 233) * 128)) * VE
We can replace a large portion of this formula with INV MAT (explained later) to yield…
GMS of Air / CYL = ((MAP - EGR) * INV MAT) * VE
* MAP is the MAP stored at L0079 that is calculated via (((A/D MAP/694) * 65536)+2647)/256. This particular calculation is located at LB5F5 in both the ANHT and the AUJP. As far as I can tell, the A/D MAP in this calculation is the actual kPa.
* EGR is the Partial Pressure due to EGR stored in L0069 and calculated at LB64E in both the ANHT and AUJP.
* INV MAT is a term that incorporates the Manifold Absolute Temperature and the Cylinder Volume (constant at 86DD) into one constant for easy calculations. To be more specific, INV MAT is CYL VOL/((MAT + 233) * 128) where MAT is the MAT counts as retrieved from the “MAT Compensation Counts vs. MAT” table located at 87FD. INV MAT is calculated at LD7FC in ANHT and at LD804 in AUJP.
*VE is the filtered Volumetric Efficiency that we discussed earlier that is stored at L0067.
Thus, everything is available to calculate the GMS of Air / CYL. This value is calculated and stored in L006F.
At this point in the conversation we have…
1) Target, theoretical AFR
2) GMS of Air / CYL
3) BLM of 128 or higher
4) INT of 128
To calculate the actual BPW all we need is the injector flow rate that is located in 841C. From this #/hr flow rate we can calculate the grams / second flow rate which is used in the following formula:
BPW = GMS AIR / (AFR * Injector Flow)
Finally, the BLM and INT is applied to the BPW to achieve the overall PW that is used at WOT. Note that the INT makes no change in the BPW because it was forced to 128.
In conclusion, the target AFR is a huge factor in determining the overall BPW. This target AFR is independent of the O2 sensor and is just a hypothetical value that the ECM is trying to achieve. This hypothetical value assumes that the VE table values will produce a 14.7:1 AFR. This 14.7:1 AFR is then modified via the PE vs. Coolant and PE vs. RPM tables and then applied to the overall Grams of Air that the engine is currently consuming. Given that we can calculate a target AFR based on the RPM and Coolant Modifiers it becomes simple enough to look at the overall AFRs that GM was shooting for as shown in the attached picture.
Tim
At this point in the discussion we have established 2 things:
1) There is a calculated, target, theoretical AFR stored in L00F1 that will be used for determining the BPW.
2) The ECM has determined the BLM that will be applied to the BPW (which will be 128 or higher).
One of the first interesting points to mention before we get to the BPW calculations is that several tests are done starting at LCA2F in ANHT and at LCA37 in AUJP. These tests forward the execution of code to a section which forces an INT of 128. These conditions are…
a) If the ECM is not in Closed Loop
b) If the ECM is in DFCO
c) If the ECM is in Power Enrichment Mode
d) If Highway Mode is enabled.
Since the ECM is in Power Enrichment (given our current conversation) then the INTegrator is forced to 128. This means that no adjustments to BPW will be done based on INT values. The section of code that forces an INT of 128 can be found at LCA85 in ANHT and at LCABD in AUJP. After forcing the INT to 128 the execution of code is forwarded to LCBD9 in ANHT and LCBE1 in AUJP. This means that we end up skipping a whole host of code that is analyzing O2 sensor readings as well as INTegrator update logic. We arrive at a point in the code that retrieves the Volumetric Efficiency (VE) from the VE tables using the current MAP and RPM. An explanation of the routine that retrieves the VE using the current MAP and RPM was explained previously HERE. After retrieving the VE the code then applies the Barometric modifier located in a table at 881F. This is helpful in ensuring correct fueling at different altitudes. Conditional filtering is then applied to this VE as long as ((%TPS > 1.2% and RPM < 1200) and Old Filtered VE value <> New VE). This conditional filtering applies a lag filter routine at LE31C to arrive at a filtered VE based off of the VE calculated after applying the Barometric modifier. The end result is that the current VE is stored in L0067. This is the VE that will be used in calculating the BPW.
We are now at a point in the code where all of the work is done for calculating the BPW. In the ANHT_HAC this is labeled at “CALCULATE SPEED DENSITY” and is located at LCC36. In AUJP it starts at LCC3E. This routine determines the Grams of Air per Cylinder (GMS of Air / CYL) according to the ideal gas law. The ideal gas law states that …
PV=nRT (or rewritten as n = PV/RT)
P = Pressure
V = Volume
n = Number of moles of gas present
R = Universal Gas Constant
T = Temperature
It is easy to see how the ideal gas law can be applied to automobiles since we are trying to determine the moles of air per cylinder which in turn yields the Grams of air per cylinder. The ANHT_HAC yields the following formula…
GMS of Air / CYL = ((MAP - EGR part press) * CYL VOL)/((MAT + 233) * 128)) * VE
We can replace a large portion of this formula with INV MAT (explained later) to yield…
GMS of Air / CYL = ((MAP - EGR) * INV MAT) * VE
* MAP is the MAP stored at L0079 that is calculated via (((A/D MAP/694) * 65536)+2647)/256. This particular calculation is located at LB5F5 in both the ANHT and the AUJP. As far as I can tell, the A/D MAP in this calculation is the actual kPa.
* EGR is the Partial Pressure due to EGR stored in L0069 and calculated at LB64E in both the ANHT and AUJP.
* INV MAT is a term that incorporates the Manifold Absolute Temperature and the Cylinder Volume (constant at 86DD) into one constant for easy calculations. To be more specific, INV MAT is CYL VOL/((MAT + 233) * 128) where MAT is the MAT counts as retrieved from the “MAT Compensation Counts vs. MAT” table located at 87FD. INV MAT is calculated at LD7FC in ANHT and at LD804 in AUJP.
*VE is the filtered Volumetric Efficiency that we discussed earlier that is stored at L0067.
Thus, everything is available to calculate the GMS of Air / CYL. This value is calculated and stored in L006F.
At this point in the conversation we have…
1) Target, theoretical AFR
2) GMS of Air / CYL
3) BLM of 128 or higher
4) INT of 128
To calculate the actual BPW all we need is the injector flow rate that is located in 841C. From this #/hr flow rate we can calculate the grams / second flow rate which is used in the following formula:
BPW = GMS AIR / (AFR * Injector Flow)
Finally, the BLM and INT is applied to the BPW to achieve the overall PW that is used at WOT. Note that the INT makes no change in the BPW because it was forced to 128.
In conclusion, the target AFR is a huge factor in determining the overall BPW. This target AFR is independent of the O2 sensor and is just a hypothetical value that the ECM is trying to achieve. This hypothetical value assumes that the VE table values will produce a 14.7:1 AFR. This 14.7:1 AFR is then modified via the PE vs. Coolant and PE vs. RPM tables and then applied to the overall Grams of Air that the engine is currently consuming. Given that we can calculate a target AFR based on the RPM and Coolant Modifiers it becomes simple enough to look at the overall AFRs that GM was shooting for as shown in the attached picture.
Tim
Last edited by TRAXION; 12-12-2003 at 09:41 AM.
12-11-2003, 02:44 PM
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Couple of quick ones:
Why would the AFR in the chart go from VERY rich to 12.2 ?
Isn't the idea to go from 14.7 to ~12.2 (the higher the rpm)?
When PE is engaged, and the INT and BLM is forced to 128, are you saying that the ECM uses the cells AND the PE table's together to achieve the target afr, or just one or the other?
I hope the ?? 's dont seem too ingnorant!
Why would the AFR in the chart go from VERY rich to 12.2 ?
Isn't the idea to go from 14.7 to ~12.2 (the higher the rpm)?
When PE is engaged, and the INT and BLM is forced to 128, are you saying that the ECM uses the cells AND the PE table's together to achieve the target afr, or just one or the other?
I hope the ?? 's dont seem too ingnorant!
12-11-2003, 03:08 PM
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Originally posted by 1bad91Z
Couple of quick ones:
Why would the AFR in the chart go from VERY rich to 12.2 ?
Isn't the idea to go from 14.7 to ~12.2 (the higher the rpm)?
I hope the ?? 's dont seem too ingnorant!
Couple of quick ones:
Why would the AFR in the chart go from VERY rich to 12.2 ?
Isn't the idea to go from 14.7 to ~12.2 (the higher the rpm)?
I hope the ?? 's dont seem too ingnorant!
Afr would be told to go richest in the TORQUE LUMP. Look where it is richest and think TPI. Make a graph of a normal-temperature column and it looks like a dyno-sheet torque curve! this gives you an insight into tuning the PE adder. Remember that the factory wants things on the SAFE side - away from LEAN but not so harsh that the cyls get scrubbed. the extra fuel at the HOT temperatures is in hopes to provide a cooling effect I suppose.
I'll leave the rest to the author... VERY NICE TIM!
Last edited by Lumberg; 12-11-2003 at 03:20 PM.
12-11-2003, 03:20 PM
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Originally posted by 1bad91Z
Couple of quick ones:
Why would the AFR in the chart go from VERY rich to 12.2 ?
Isn't the idea to go from 14.7 to ~12.2 (the higher the rpm)?
When PE is engaged, and the INT and BLM is forced to 128, are you saying that the ECM uses the cells AND the PE table's together to achieve the target afr, or just one or the other?
Couple of quick ones:
Why would the AFR in the chart go from VERY rich to 12.2 ?
Isn't the idea to go from 14.7 to ~12.2 (the higher the rpm)?
When PE is engaged, and the INT and BLM is forced to 128, are you saying that the ECM uses the cells AND the PE table's together to achieve the target afr, or just one or the other?
Assuming Closed Loop, the target AFR is calculated only via the PE Tables (RPM and Coolant) and the stoichiometric constant. The VE table values are not used and are not needed for calculating a target AFR. They are used when calculating the Grams of Air per Cylinder. This is a lot to digest. However, everything should become pretty clear after reading it about 10 times - lol.
Tim
12-11-2003, 03:23 PM
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BTW - I really encourage anyone good with assembly to please look through what I have written and to correct any of my mistakes. I make absolutely no claim as to this being 100% correct since I am not an assembly expert 
Tim
Tim
12-11-2003, 04:00 PM
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It's starting to makes sense. I've soaked up alot in the last month.
(The whole PROM and all of it's tables) are quite alot of stuff to digest!
Great info though Trax!
(The whole PROM and all of it's tables) are quite alot of stuff to digest!
Great info though Trax!
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12-11-2003, 06:01 PM
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trax this is kick ***. good work. as far as i can tel everything you posted appears to be correct. im nto sure if all the ram adress's for stored values are but the whole Thoery of how it works is 100% on target. SWEETT !! im glad you figured out how to write this up. id been trying to figure it out for a long time hw to write it up.
GOOD WORK !!!!!!!
GOOD WORK !!!!!!!
12-11-2003, 07:49 PM
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Assuming Closed Loop, the target AFR is calculated only via the PE Tables (RPM and Coolant) and the stoichiometric constant. The VE table values are not used and are not needed for calculating a target AFR. They are used when calculating the Grams of Air per Cylinder.
12-11-2003, 08:28 PM
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Originally posted by 11sORbust
could you explain or point me to the area that explains that. Cause I could ask a dumb question but I think I'll just read everything again.
could you explain or point me to the area that explains that. Cause I could ask a dumb question but I think I'll just read everything again.
This stoichiometric starting value is loaded into memory during the PE routine of the code at LC823 in ANHT and at LC82B in AUJP. The code then modifies this stoichiometric value according to the PE Modifiers (PE %Change to AFR vs. RPM table at L8617 and PE %Change to AFR vs. Coolant table at L860D). This modification is completed according to the following formula:
WOT AFR = 6553.6 / (((TBL L8617 + TBL L860D + 128) * 445) / 256)
WOT AFR = 6553.6 / (((TBL L8617 + TBL L860D + 128) * 445) / 256)
WOT AFR = Stoichiometric Constant / (LAMBDA C + LAMBDA W)
LAMBDA C = Decimal value for PE %Change to Fuel/Air Ratio vs. Coolant Temp. which has been modified by dividing by 256.
LAMBDA C = TBL L860D / 256
LAMBDA W = Decimal value for PE %Change to Fuel/Air Ratio vs. RPM which has been modified by dividing by 256 and adding 0.5
LAMBDA W = (TBL L8617 / 256) + 0.5
Using our original values from the first equation we can calculate the AFR again...
WOT AFR = 14.7 / ( (TBL L860D / 256) + (TBL L8617 / 256) + 0.5) )
WOT AFR = 14.7 / ( (58 / 256) + (148 / 256) + 0.5) )
WOT AFR = 14.7 / (0.227 + 1.078)
WOT AFR = 11.3 (same as before)
Tim
12-11-2003, 08:53 PM
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Originally posted by 11sORbust
I'm sorry but I have a dumb question. If I change the stioch a/f ratio constant will that effect wot PW calculation? sorry...
I'm sorry but I have a dumb question. If I change the stioch a/f ratio constant will that effect wot PW calculation? sorry...
In my post I indicate that the BPW is calculated according to ..
BPW = (GMS AIR * AFR) / Injector Flow
AFR is the target AFR.
The target AFR is determined by modifying the stoich AFR with the PE modifiers.
So, yes, according to the code, if you change the stoichiometric AFR then you will change the BPW. I have not tested this in the real world yet. It's just code analysis. This is where an ECM bench is worth it's weight in gold. I wish I had enough money to buy one of Saturn5's boards
Tim
12-11-2003, 10:15 PM
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another question, If I change the stoich constant to lets say 13.5, how will that effect blm calculation? Will 128 int/blm=13.5 or will the ecm stop compensating part throttle at the blm number that equils 13.5 a/f ratio? OR does the stoich constant not effect blm calculation? Sorry to venture off topic. But the stoich constant table didn't do much of anything, the last time I asked(a long time ago). Now you confirm that the constant effects wot(untested). I have always thought that constant had effect on blm calculations,somehow. I could be wrong and sound like a tard. It seems like half the time your response is WTF.
12-12-2003, 07:28 AM
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The stoich constant matches the fuel being used. If in a country that uses 100% ethanol then it would be set to 6.0 or there abouts. Now the calculated PW will be correct for the amount of fuel required for a stoich mixture.
The PE adders would then modify this stoich AFR for more fuel to obtain the required AFR for rich best power.
The BLM value (and INTeger) are based on the O2 sensor. If you set the stoich value to 13.5 and run gasoline the O2 sensor will cause the BLM to drop bringing the actual AFR back to true stoich of 14.7 due to a decreased PW.
If using 100% ethanol (we moved to Brazil) then the O2 sensor would bring the INT & BLM in line with the stoich AFR for ethonal, ca 6.0:1.
RBob.
The PE adders would then modify this stoich AFR for more fuel to obtain the required AFR for rich best power.
The BLM value (and INTeger) are based on the O2 sensor. If you set the stoich value to 13.5 and run gasoline the O2 sensor will cause the BLM to drop bringing the actual AFR back to true stoich of 14.7 due to a decreased PW.
If using 100% ethanol (we moved to Brazil) then the O2 sensor would bring the INT & BLM in line with the stoich AFR for ethonal, ca 6.0:1.
RBob.
12-12-2003, 07:44 AM
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Tim,
I'm not 100% sure how that would affect BLM calculation. From what RBob has posted in the past it would seem that the O2 voltage constants in the BIN have something to do with it. However, I haven't attacked that portion of the code yet.
I'm more than willing to tell you what I do know. First and foremost, we need to set some ground rules. You are speaking about part throttle because, as far as I can tell, BLM calculation isn't done at WOT. It may use a lean BLM (> 128) but it's not calculating any new BLMs. Since that question doesn't have anything to do with this post I would suggest making a new post entitled "How does the Stoichiometric constant affect part throttle BLMs in $8D?"
Now a quick comment on my WTF responses,
I only respond WTF mainly when someone asks a question where I already stated the answer
Sometimes I feel like my words fall on deaf ears when someone asks a question where my reply to that question is a cut and paste from my previous post. Part of this is me spending a lot of time figuring things out ... to then be asked a question where the answer is already clearly stated. This is probably due to the fact that I am thinking "I spend all this time figuring things out, taking notes, organizing, reading, researching ... and people just won't take the time to read what I wrote a few times AND to really try to understand it before asking questions". I am all for asking questions. I just want people to put some time into thinking. If I put a lot of time to bring some information to the board then I only ask 2 things in return ...
1) Someone doesn't ask a question where my response will be a cut and paste.
2) If it's 95 degrees out, please don't ask why isn't it snowing (recent example is when somebody asked me if they STILLneeded to plug their wideband into the ECM and run the wideband hac in order to view the wideband AFR in datamaster when running the IM wideband kit . Ummmm - if you didn't then how would the IM signal get to the ALDL stream. How would the signal be interpreted? Does the signal stream through thin air and then g0d interprets it? lol)
Tim
I'm not 100% sure how that would affect BLM calculation. From what RBob has posted in the past it would seem that the O2 voltage constants in the BIN have something to do with it. However, I haven't attacked that portion of the code yet.
I'm more than willing to tell you what I do know. First and foremost, we need to set some ground rules. You are speaking about part throttle because, as far as I can tell, BLM calculation isn't done at WOT. It may use a lean BLM (> 128) but it's not calculating any new BLMs. Since that question doesn't have anything to do with this post I would suggest making a new post entitled "How does the Stoichiometric constant affect part throttle BLMs in $8D?"
Now a quick comment on my WTF responses,
I only respond WTF mainly when someone asks a question where I already stated the answer
Sometimes I feel like my words fall on deaf ears when someone asks a question where my reply to that question is a cut and paste from my previous post. Part of this is me spending a lot of time figuring things out ... to then be asked a question where the answer is already clearly stated. This is probably due to the fact that I am thinking "I spend all this time figuring things out, taking notes, organizing, reading, researching ... and people just won't take the time to read what I wrote a few times AND to really try to understand it before asking questions". I am all for asking questions. I just want people to put some time into thinking. If I put a lot of time to bring some information to the board then I only ask 2 things in return ...1) Someone doesn't ask a question where my response will be a cut and paste.
2) If it's 95 degrees out, please don't ask why isn't it snowing (recent example is when somebody asked me if they STILLneeded to plug their wideband into the ECM and run the wideband hac in order to view the wideband AFR in datamaster when running the IM wideband kit . Ummmm - if you didn't then how would the IM signal get to the ALDL stream. How would the signal be interpreted? Does the signal stream through thin air and then g0d interprets it? lol)
Tim
12-12-2003, 08:10 AM
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Hey RBob,
Did I get this correct?
BPW = (GMS AIR * AFR) / Injector Flow
From your post it would seem that maybe I have it wrong since DECREASING the AFR should yield a greater pulse width. Seems like it should be...
BPW = GMS AIR / (AFR * Injector Flow)
??
Tim
Did I get this correct?
BPW = (GMS AIR * AFR) / Injector Flow
From your post it would seem that maybe I have it wrong since DECREASING the AFR should yield a greater pulse width. Seems like it should be...
BPW = GMS AIR / (AFR * Injector Flow)
??
Tim
12-12-2003, 09:20 AM
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Originally posted by TRAXION
Hey RBob,
Did I get this correct?
BPW = (GMS AIR * AFR) / Injector Flow
From your post it would seem that maybe I have it wrong since DECREASING the AFR should yield a greater pulse width. Seems like it should be...
BPW = GMS AIR / (AFR * Injector Flow)
??
Tim
Hey RBob,
Did I get this correct?
BPW = (GMS AIR * AFR) / Injector Flow
From your post it would seem that maybe I have it wrong since DECREASING the AFR should yield a greater pulse width. Seems like it should be...
BPW = GMS AIR / (AFR * Injector Flow)
??
Tim
The ratio of Air to Fuel. From the looks of the $8D code the AFR term is actually the inverse or the FA ratio. Hence the confusion.
RBob.
12-12-2003, 09:43 AM
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Thanks RBob,
I updated the initial post to show the correct formula. At least I caught one of my mistakes. Did you notice any others that you wouldn't mind commenting on and showing my stupidity? I often wear a CSH when going through assembly.
Tim
I updated the initial post to show the correct formula. At least I caught one of my mistakes. Did you notice any others that you wouldn't mind commenting on and showing my stupidity? I often wear a CSH when going through assembly.
Tim
12-12-2003, 11:04 AM
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The second has to be right. The first is air*air/fuel*fuel. The second is air*fuel/air*fuel. There's no air^2 or fuel^2 units on the left side, only time.
Just a little nobrainer for those having a bad day or dont know, 14.7:1= 14.7air/1fuel Follow your units and you can verify that you're at least coming up with a useful number. If the units are wrong, so is your number (and formula).
Just a little nobrainer for those having a bad day or dont know, 14.7:1= 14.7air/1fuel Follow your units and you can verify that you're at least coming up with a useful number. If the units are wrong, so is your number (and formula).
12-12-2003, 12:05 PM
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Originally posted by madmax
The second has to be right. The first is air*air/fuel*fuel. The second is air*fuel/air*fuel. There's no air^2 or fuel^2 units on the left side, only time.
Just a little nobrainer for those having a bad day or dont know, 14.7:1= 14.7air/1fuel Follow your units and you can verify that you're at least coming up with a useful number. If the units are wrong, so is your number (and formula).
The second has to be right. The first is air*air/fuel*fuel. The second is air*fuel/air*fuel. There's no air^2 or fuel^2 units on the left side, only time.
Just a little nobrainer for those having a bad day or dont know, 14.7:1= 14.7air/1fuel Follow your units and you can verify that you're at least coming up with a useful number. If the units are wrong, so is your number (and formula).
That's exactly how I figured out my mistake after seeing what RBob posted. I remember my teacher always enforcing the "Factor Label Method" of writing out the units so they cancel each other. Wooo woooooooooo!Tim
12-16-2003, 08:49 AM
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The target AFR for WOT should not be confused with stoichiometric AFR. The following is a quote from an ex-Lotus/GM calibration engineer on this topic.
Quote
There are a few inconsistencies in the text, I
think he is using the term stoichiometric AFR incorrectly. Stoich combustion
refers to the AFR where complete ideal combustion takes place which is 14.7:1. Most engines of the LT5/L98/LT1 vintage cannot run stoich when
approaching WOT max power/torque for various reasons. The main reason is
component protection i.e. the valves, valve seats (max temp 850degC) and
catalysts(max temp <1000degC). The ceramic monolith catalysts will not stand
the high exhaust temperatures created when running stoich at WOT. Fuel is
used as a cooling medium to keep the temps below 1000degC so 12.5:1 is not
uncommon. The base PE table is used to make sure that the engine is rich
enough under high load conditions.
Unquote
He did not go into why the 14.7 figure was used as a base starting point but his point is when we go PE stoich afr is inconsistent with the remaining discussion, in fact the calculations go to great lengths to factor out any values that would result in stocih afr being used to calculate bpw.
The afr in PE is not a theoretical figure, it is a figure arrived at using dyno work for the engine/trans certification process for emissions and engine durability. In your discussion the better term would be base afr and even though it is the same as stoich it does not have the same conotation in this context.
Tyler
Quote
There are a few inconsistencies in the text, I
think he is using the term stoichiometric AFR incorrectly. Stoich combustion
refers to the AFR where complete ideal combustion takes place which is 14.7:1. Most engines of the LT5/L98/LT1 vintage cannot run stoich when
approaching WOT max power/torque for various reasons. The main reason is
component protection i.e. the valves, valve seats (max temp 850degC) and
catalysts(max temp <1000degC). The ceramic monolith catalysts will not stand
the high exhaust temperatures created when running stoich at WOT. Fuel is
used as a cooling medium to keep the temps below 1000degC so 12.5:1 is not
uncommon. The base PE table is used to make sure that the engine is rich
enough under high load conditions.
Unquote
He did not go into why the 14.7 figure was used as a base starting point but his point is when we go PE stoich afr is inconsistent with the remaining discussion, in fact the calculations go to great lengths to factor out any values that would result in stocih afr being used to calculate bpw.
The afr in PE is not a theoretical figure, it is a figure arrived at using dyno work for the engine/trans certification process for emissions and engine durability. In your discussion the better term would be base afr and even though it is the same as stoich it does not have the same conotation in this context.
Tyler
12-23-2003, 06:40 PM
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As per what RBob posted ...
I completed this modification to the code and it works Great! Thanks again RBob!
Tim
If you want to lock the BLM at 128 whenever in PE mode change these two locations to $01:
$49B3 and $49B4
A $01 is a NOP and will eliminate the BMI instruction. The 128 will always be loaded and used when in PE mode.
Note that those locations are for AUJP, other BCC's may vary.
$49B3 and $49B4
A $01 is a NOP and will eliminate the BMI instruction. The 128 will always be loaded and used when in PE mode.
Note that those locations are for AUJP, other BCC's may vary.
Tim
12-23-2003, 06:46 PM
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I disabled the chance of the ECM using open loop AFRs instead of the closed loop AFRs. I did this by setting locations 4837 through 4841 to NOP commands ... '01'. This is for AUJP. Not sure about other BCCs.
Tim
Tim
12-23-2003, 11:33 PM
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Hey Tim. How did you change this code? Via the PP2 edit buffer method or otherwise? I appreciate any help.
12-24-2003, 07:51 AM
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I did it by using a hex editor. Specifically, I use XVI32 ...
http://www.chmaas.handshake.de/delph...vi32/xvi32.htm
The important thing here is that after you modify the bin using a hex editor that you then reopen the bin in your favorite Tuner program like TunerCat or TunerPro and then resave the BIN to force a recalculation of the checksum.
Tim
http://www.chmaas.handshake.de/delph...vi32/xvi32.htm
The important thing here is that after you modify the bin using a hex editor that you then reopen the bin in your favorite Tuner program like TunerCat or TunerPro and then resave the BIN to force a recalculation of the checksum.
Tim
12-24-2003, 11:47 AM
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OK Tim let me know if this is right. I have XVI32 and have opened a .bin and went to address-goto hex location $4837. The location is labeled to the left as 482F and the cursor is in a cell reading 1A. Is this correct and do I change 1A to 01? I am trying to learn this. Sorry about the questions but we all have to start somewhere.
12-29-2003, 01:36 AM
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Since we're talking about the "730" computer, i scaned a 1990 IROC with a 383 and a 224/230 comp cam. The spark advance my AUTO-XRAY was showing with the TPIS chip was 29.9 degrees W.O.T., it could have been as low as 3500 rpms on up, the spark advanced was maxed.The stock chip added spark up the rpm range to i think 32 degrees possibly more. My question is, is this reading total spark advance including the 6 degrees base timming, or just computer advance where you would add the base advance to total timming?
12-29-2003, 06:44 AM
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Originally posted by hvymtl
Since we're talking about the "730" computer, i scaned a 1990 IROC with a 383 and a 224/230 comp cam. The spark advance my AUTO-XRAY was showing with the TPIS chip was 29.9 degrees W.O.T., it could have been as low as 3500 rpms on up, the spark advanced was maxed.The stock chip added spark up the rpm range to i think 32 degrees possibly more. My question is, is this reading total spark advance including the 6 degrees base timming, or just computer advance where you would add the base advance to total timming?
Since we're talking about the "730" computer, i scaned a 1990 IROC with a 383 and a 224/230 comp cam. The spark advance my AUTO-XRAY was showing with the TPIS chip was 29.9 degrees W.O.T., it could have been as low as 3500 rpms on up, the spark advanced was maxed.The stock chip added spark up the rpm range to i think 32 degrees possibly more. My question is, is this reading total spark advance including the 6 degrees base timming, or just computer advance where you would add the base advance to total timming?
Tim
Last edited by TRAXION; 12-29-2003 at 06:57 AM.
12-29-2003, 06:40 PM
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I forget what Mask it was, but in the ALDL data stream they used a spark value that was before being used in the routine for set max timing routine. So you saw the higher numbers, which we not the final spark value.
Again, the need for an accurate Source Code is what matters alot. THEN you can intelligently modify it.
Again, the need for an accurate Source Code is what matters alot. THEN you can intelligently modify it.
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Re: P730: Target AFR and how it is used in PE Mode
So in practice what does everyone do here? Adjust the PE %Change to Fuel/Air Ratio vs. RPM so that it is a flat 12.5-12.7? Or do people actually try and go even richer at the torque peaks like the factory did?
10-08-2008, 01:00 AM
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Re: P730: Target AFR and how it is used in PE Mode
I too would like to know the preferred method of tunning wot.
I was able to get my car to ~12.9 on the WB02. However, the commanded AFR was 11.3.
Would I apply a 14% increase to the VE table in that region, then set the PE % change in AFR table so that it would reflect a commanded AFR of 12.9 across the range? Unfortunately, doing so yields VE cells over 100.
My injectors flow rate in the bin is if anything, lower than actual flow rate. I even have the cylinder volume adjusted for the 0.030 over bore giving 722cc/cyl as compared to the 713cc/cyl originally in SaujpV4.
I'm scratching my head here as to what I should do next. I am pretty much dialed in to the AFR I would like to achieve under WOT. However, I would like to see some other input for the best way to do this.
Thanks in advance
I was able to get my car to ~12.9 on the WB02. However, the commanded AFR was 11.3.
Would I apply a 14% increase to the VE table in that region, then set the PE % change in AFR table so that it would reflect a commanded AFR of 12.9 across the range? Unfortunately, doing so yields VE cells over 100.
My injectors flow rate in the bin is if anything, lower than actual flow rate. I even have the cylinder volume adjusted for the 0.030 over bore giving 722cc/cyl as compared to the 713cc/cyl originally in SaujpV4.
I'm scratching my head here as to what I should do next. I am pretty much dialed in to the AFR I would like to achieve under WOT. However, I would like to see some other input for the best way to do this.
Thanks in advance
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