Regular vs Premium unleaded Fuel - Stoich AFR
Discussion
For anyone with Efilive or HPTuners performing autoVE its worth noting the stoich AFR of premium fuels are around 14.4:1, regular is around 14.7:1.
Source: http://www.bp.com/content/dam/bp-country/en_au/med...
Its worthwhile setting calibration {B3671} LS2 or {B3601} LS1, from 14.7:1 stock to the stoich AFR for the fuel generally used so as not to screw up VE or MAF tuning process.
Source: http://www.bp.com/content/dam/bp-country/en_au/med...
Its worthwhile setting calibration {B3671} LS2 or {B3601} LS1, from 14.7:1 stock to the stoich AFR for the fuel generally used so as not to screw up VE or MAF tuning process.
Edited by Gelf VXR on Wednesday 28th October 23:50
MyM8V8 said:
Good point!
(Then we should just be doing VE on the regular?)
This is what I don't get - if using a wideband for VE then you're just tuning to non-stoich aren't you? There are regions of the VE table that you won't reach out of PE anyway, but it's just implicitly corrected using BEN. (Then we should just be doing VE on the regular?)
What are the consequences of using 14.7/14.63 as the nominal stoich instead of 14.4 regarding power/emissions? I'm assuming not much on power, as if you're commanding stoich then (for NA at least) the spark timing seems more responsive/sensitive than commanding more fuel.
Can read more about in this thread https://forum.efilive.com/showthread.php?11752-usi...
QUOTE=eficalibrator
Ideally, you just set your defined stoich point in the table to whatever the chemistry of your fuel really is and leave it alone. (I use 14.13 for e10, 14.64 for "normal" gasoline, and 14.4 to split the difference if we're unsure of what's in the tank)
Once you've defined the stoich point, you work entirely in units of lambda or EQR for relative richness. A value of 1.0 should command whatever your predefined stoich point is for delivered AFR on the scanner. If this really matches your fuel in the tank and you've nailed both the injector tables (ALL of them) along with the airflow models, your fuel trims will be very close to zero and everything works as intended.
I can confirm that adjusting the stoich point scalar/table will indeed change the open loop fuel delivery as well as the displayed "commanded AFR" on the scanner.
When using ethanol blends (including e10), you have to break the habit of saying "I want 12.6:1 at WOT" and start thinking "I want lambda 0.86 (or 1.16 EQR) at WOT." It's the same RELATIVE enrichment, from a different stoich point; and that's all the combustion in the cylinder cares about.
Likewise, you also need to log LAMBDA or EQR from the wideband, NOT AFR. If you calculate fueling errors based on displayed AFR on the wideband divided by some modified stoich, you're asking for trouble. Further, most widebands display "AFR" by merely multiplying actual lambda by 14.64ish, which means that a displayed "14.64" on that wideband would REALLY be 14.13 for e10, since that's lambda=1.00 at the sensor. See where these start to compound? Using the "BEN factor" based on AFR just takes you a step further toward confusion in this case. That's why I log exclusively in lambda, and view GM cal tables in EQR to stay consistent even when stoich for the fuel is different.
QUOTE=eficalibrator
Ideally, you just set your defined stoich point in the table to whatever the chemistry of your fuel really is and leave it alone. (I use 14.13 for e10, 14.64 for "normal" gasoline, and 14.4 to split the difference if we're unsure of what's in the tank)
Once you've defined the stoich point, you work entirely in units of lambda or EQR for relative richness. A value of 1.0 should command whatever your predefined stoich point is for delivered AFR on the scanner. If this really matches your fuel in the tank and you've nailed both the injector tables (ALL of them) along with the airflow models, your fuel trims will be very close to zero and everything works as intended.
I can confirm that adjusting the stoich point scalar/table will indeed change the open loop fuel delivery as well as the displayed "commanded AFR" on the scanner.
When using ethanol blends (including e10), you have to break the habit of saying "I want 12.6:1 at WOT" and start thinking "I want lambda 0.86 (or 1.16 EQR) at WOT." It's the same RELATIVE enrichment, from a different stoich point; and that's all the combustion in the cylinder cares about.
Likewise, you also need to log LAMBDA or EQR from the wideband, NOT AFR. If you calculate fueling errors based on displayed AFR on the wideband divided by some modified stoich, you're asking for trouble. Further, most widebands display "AFR" by merely multiplying actual lambda by 14.64ish, which means that a displayed "14.64" on that wideband would REALLY be 14.13 for e10, since that's lambda=1.00 at the sensor. See where these start to compound? Using the "BEN factor" based on AFR just takes you a step further toward confusion in this case. That's why I log exclusively in lambda, and view GM cal tables in EQR to stay consistent even when stoich for the fuel is different.
Again it really doesnt matter. Whether lambda, AFR, or plain raw voltages.
The sensor output is not lambda, it's voltage/current...this is then converted to give you a number you're happy to see. Some will prefer a lambda value, some will prefer an AFR value. It really doesnt matter a single bit.
If you're using normal fuel at say 14.7:1, then doesnt matter what mix of fuel you're using, stioch will always display as 14.7, in exactly the same way Lambda will always display as 1.
Just use the numbers you're happy and comfortable with, they're all generated on your chosen display purely for that reason anyway
It really isnt a big deal so no need to overthink it.
The sensor output is not lambda, it's voltage/current...this is then converted to give you a number you're happy to see. Some will prefer a lambda value, some will prefer an AFR value. It really doesnt matter a single bit.
If you're using normal fuel at say 14.7:1, then doesnt matter what mix of fuel you're using, stioch will always display as 14.7, in exactly the same way Lambda will always display as 1.
Just use the numbers you're happy and comfortable with, they're all generated on your chosen display purely for that reason anyway
It really isnt a big deal so no need to overthink it.
stevieturbo said:
Again it really doesnt matter. Whether lambda, AFR, or plain raw voltages.
The sensor output is not lambda, it's voltage/current...this is then converted to give you a number you're happy to see. Some will prefer a lambda value, some will prefer an AFR value. It really doesnt matter a single bit.
If you're using normal fuel at say 14.7:1, then doesnt matter what mix of fuel you're using, stioch will always display as 14.7, in exactly the same way Lambda will always display as 1.
Just use the numbers you're happy and comfortable with, they're all generated on your chosen display purely for that reason anyway
It really isnt a big deal so no need to overthink it.
I agree if your using regular fuel nothing to be done, however the point that I made was to calibrate the PCM to the correct stoich value for the fuel in the tank, if its not the same all open loop and PE calculations will be off by the error, for example The sensor output is not lambda, it's voltage/current...this is then converted to give you a number you're happy to see. Some will prefer a lambda value, some will prefer an AFR value. It really doesnt matter a single bit.
If you're using normal fuel at say 14.7:1, then doesnt matter what mix of fuel you're using, stioch will always display as 14.7, in exactly the same way Lambda will always display as 1.
Just use the numbers you're happy and comfortable with, they're all generated on your chosen display purely for that reason anyway
It really isnt a big deal so no need to overthink it.
if the PCM is calibrated 14.7 and you want to command PE 0.85 lambda
14.7 * 0.85 = 12.495 AFR
if the true stoich AFR is 14.4, then what you will command is
14.4 * 0.85 = 12.24 AFR
A 2.1% error
Again in Auto VE, using wideband O2's, if your correction calculations use AFR, commanded AFR / Wide Band AFR your BEN factor corrections will be wrong if the true stoich AFR is 14.4 and the correction calculation uses 14.7.
A 2.1% error
As in my original post, to anyone who has invested in scan & tune kit and wide bands, and probably want the satisfaction of creating as good as a professional home tune as possible, its worth noting.
The sound advice quoted in my previous post is from Greg Bannish, producer of the Calibrated Success Video's and Books.
Edited by Gelf VXR on Monday 26th October 02:30
Gelf VXR said:
stevieturbo said:
Again it really doesnt matter. Whether lambda, AFR, or plain raw voltages.
The sensor output is not lambda, it's voltage/current...this is then converted to give you a number you're happy to see. Some will prefer a lambda value, some will prefer an AFR value. It really doesnt matter a single bit.
If you're using normal fuel at say 14.7:1, then doesnt matter what mix of fuel you're using, stioch will always display as 14.7, in exactly the same way Lambda will always display as 1.
Just use the numbers you're happy and comfortable with, they're all generated on your chosen display purely for that reason anyway
It really isnt a big deal so no need to overthink it.
The sound advice quoted in my previous post is from Greg Bannish, producer of the Calibrated Success Video's and Books.The sensor output is not lambda, it's voltage/current...this is then converted to give you a number you're happy to see. Some will prefer a lambda value, some will prefer an AFR value. It really doesnt matter a single bit.
If you're using normal fuel at say 14.7:1, then doesnt matter what mix of fuel you're using, stioch will always display as 14.7, in exactly the same way Lambda will always display as 1.
Just use the numbers you're happy and comfortable with, they're all generated on your chosen display purely for that reason anyway
It really isnt a big deal so no need to overthink it.
Edited by Gelf VXR on Monday 26th October 02:30
Stevie's argument makes sense to me - the sensor itself works in terms of proportion of oxygen, so EQ or lambda are the natural units. They tend to assume stoich is 14.7 so they can display an AFR, but for all intents and purposes a clean/full burn is EQ = lambda = 1 irrespective of the fuel. I can only see a problem if you're working in AFR units and have messed up the reference stoich.
Gelf VXR said:
I agree if your using regular fuel nothing to be done, however the point that I made was to calibrate the PCM to the correct stoich value for the fuel in the tank, if its not the same all open loop and PE calculations will be off by the error, for example
if the PCM is calibrated 14.7 and you want to command PE 0.85 lambda
14.7 * 0.85 = 12.495 AFR
if the true stoich AFR is 14.4, then what you will command is
14.4 * 0.85 = 12.24 AFR
A 2.1% error
Again in Auto VE, using wideband O2's, if your correction calculations use AFR, commanded AFR / Wide Band AFR your BEN factor corrections will be wrong if the true stoich AFR is 14.4 and the correction calculation uses 14.7.
A 2.1% error
As in my original post, to anyone who has invested in scan & tune kit and wide bands, and probably want the satisfaction of creating as good as a professional home tune as possible, its worth noting.
The sound advice quoted in my previous post is from Greg Bannish, producer of the Calibrated Success Video's and Books.
YOU are changing the units. The ecu hasnt been told to expect different values for stioch that YOU are changing. So it's YOU who are causing the errors here.if the PCM is calibrated 14.7 and you want to command PE 0.85 lambda
14.7 * 0.85 = 12.495 AFR
if the true stoich AFR is 14.4, then what you will command is
14.4 * 0.85 = 12.24 AFR
A 2.1% error
Again in Auto VE, using wideband O2's, if your correction calculations use AFR, commanded AFR / Wide Band AFR your BEN factor corrections will be wrong if the true stoich AFR is 14.4 and the correction calculation uses 14.7.
A 2.1% error
As in my original post, to anyone who has invested in scan & tune kit and wide bands, and probably want the satisfaction of creating as good as a professional home tune as possible, its worth noting.
The sound advice quoted in my previous post is from Greg Bannish, producer of the Calibrated Success Video's and Books.
YOU are effectively telling the ecu that lambda is now 0.98...which of course is incorrect. Lambda is 1. Stioch for the ecu in AFR numbers is 14.7.
Until you've re-programmed the ecu with different AFR/Stioch values....ie telling it the specific fuel you are using, then what YOU are doing is wrong.
Mud_ said:
Stevie's argument makes sense to me - the sensor itself works in terms of proportion of oxygen, so EQ or lambda are the natural units. They tend to assume stoich is 14.7 so they can display an AFR, but for all intents and purposes a clean/full burn is EQ = lambda = 1 irrespective of the fuel. I can only see a problem if you're working in AFR units and have messed up the reference stoich.
Late PCM have sensors to detect fuel used and compensate the stioch AFR
Gelf VXR said:
we are concerned with the PCM calibration
Exactly. And it has been told to expect fuel with a stioch of lambda 1.....and the tuning software you are using has been programmed with that stioch AFR as 14.7Now unless YOU can change that programming and tell the ecu you're using a different stioch value....then dont change things and create errors.
And I dont think any of the UK cars have a flex fuel sensor as standard ? Not that we have ethanol here anyway...and the sensor does not change stioch or lambda. It purely measures ethanol content, or what it believes to be ethanol content.
The ecu certainly doesnt care about any AFR values...that's purely the tuning software giving you the user a number system you're happy to use.
stevieturbo said:
Exactly. And it has been told to expect fuel with a stioch of lambda 1.....and the tuning software you are using has been programmed with that stioch AFR as 14.7
Now unless YOU can change that programming and tell the ecu you're using a different stioch value....then dont change things and create errors.
And I dont think any of the UK cars have a flex fuel sensor as standard ? Not that we have ethanol here anyway...and the sensor does not change stioch or lambda. It purely measures ethanol content, or what it believes to be ethanol content.
The ecu certainly doesnt care about any AFR values...that's purely the tuning software giving you the user a number system you're happy to use.
Now unless YOU can change that programming and tell the ecu you're using a different stioch value....then dont change things and create errors.
And I dont think any of the UK cars have a flex fuel sensor as standard ? Not that we have ethanol here anyway...and the sensor does not change stioch or lambda. It purely measures ethanol content, or what it believes to be ethanol content.
The ecu certainly doesnt care about any AFR values...that's purely the tuning software giving you the user a number system you're happy to use.
Do you own EFILive or hptuners
Gelf VXR said:
Do you own EFILive or hptuners
And you are changing AFR target tables, you are not talking about telling the ecu you're using a different fuel, with a completely different AFR/Stioch/Lambda reference table, and then using all these different values to achieve the same end goal...for which you actually had to do nothing at all.
stevieturbo said:
you are not talking about telling the ecu you're using a different fuel, with a completely different AFR/Stioch/Lambda reference table,
Actually I am, and so is Greg Banish in the quote advice I referenced earlier, and I referenced the PCM calibration {B3671} in my original post.See below, stoichiometric AFR value,..
Wha eve you set this to will show as the commanded AFR in closed loop.
Edited by Gelf VXR on Monday 26th October 11:42
Mud_ said:
b3671, luxury! I only have b3601.
b3601 is the equivalent LS1 calibration, the LS2 only references 0% ethanol, it doesn't have flex fuel so its set the same value throughout the table.I looked back thru my logs and determined my average stoich AFR was 14.49, using BP ultimate fuel.
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