stoichemetric afr, 93 octane 10 percent ethanol
09-09-2015, 12:29 PM
#1
stoichemetric afr, 93 octane 10 percent ethanol I'm just starting to get into tuning, and I'm reviewing my tune, my stoichemetric afr is set for 14.681. which I believe is correct for gasoline. but the 93 octane I use around here is 10% ethanol.
should I change the stoich value in my pcm to an afr that is a little more appropriate for the blended fuel? such as 14.1 ish?
should I change the stoich value in my pcm to an afr that is a little more appropriate for the blended fuel? such as 14.1 ish?
09-09-2015, 10:33 PM
#3
Moderator
If your LTFT is good, I would just leave the "stoichemetric afr" value alone, whatever it is. Correct me if I am wrong: If you lower this value, you will need to lower the entire VE table by the same percentage or you will be running rich. I am not sure about the MAF table.
If you later decide to change all your tuning to "lambda" then I would first change it to "14.11" (or something similar), adjust the VE table (and MAF?) and then make the switch.
Do you have a wideband installed already?
If you later decide to change all your tuning to "lambda" then I would first change it to "14.11" (or something similar), adjust the VE table (and MAF?) and then make the switch.
Do you have a wideband installed already?
09-11-2015, 06:30 AM
#4
If your LTFT is good, I would just leave the "stoichemetric afr" value alone, whatever it is. Correct me if I am wrong: If you lower this value, you will need to lower the entire VE table by the same percentage or you will be running rich. I am not sure about the MAF table.
If you later decide to change all your tuning to "lambda" then I would first change it to "14.11" (or something similar), adjust the VE table (and MAF?) and then make the switch.
Do you have a wideband installed already?
If you later decide to change all your tuning to "lambda" then I would first change it to "14.11" (or something similar), adjust the VE table (and MAF?) and then make the switch.
Do you have a wideband installed already?
09-11-2015, 11:08 AM
#5
An odd thing to remember. No matter what fuel you are using, stoich is ~14.63. The Lambda if very different between fuels BUT an o2 sensor measures o2 not fuel content.
If you change nothing in the car but the fuel to say E85, until the trims try to fix it you will be VERY lean. If the trims can bring it back in line the o2 will read 14.63 again.
Changing the stoich value in the OS should allow you to run E10 or E85 without messing with the tune. This is in an ideal world scenario and will never happen. Some tuning will still be required.
If you change nothing in the car but the fuel to say E85, until the trims try to fix it you will be VERY lean. If the trims can bring it back in line the o2 will read 14.63 again.
Changing the stoich value in the OS should allow you to run E10 or E85 without messing with the tune. This is in an ideal world scenario and will never happen. Some tuning will still be required.
09-11-2015, 01:18 PM
#6
Moderator
Exidous: I'm sure you understand the topic but just aren't wording it correctly. Your "No matter what fuel you are using, stoich is ~14.63." is blatantly false the way most people would interpret it.
The rest of your post is fine.
A wideband O2 gauge set to AFR values will show 14.63 at stoich, regardless of fuel, because it is really reading 1.0 lambda.
Therefore, please edit your post to read correctly. Keep in mind that hundreds, if not thousands of people will read this thread in the future due to a Google search, and accuracy in wording is important.
Thank you.
The rest of your post is fine.
A wideband O2 gauge set to AFR values will show 14.63 at stoich, regardless of fuel, because it is really reading 1.0 lambda.
Therefore, please edit your post to read correctly. Keep in mind that hundreds, if not thousands of people will read this thread in the future due to a Google search, and accuracy in wording is important.
Thank you.
Trending Topics
09-15-2015, 01:00 PM
#9
thanks guys, this has turned into a really informative thread, great info.
as a follow up question. should I change my "stoich afr" table in hp tuners to reflect e10 fuel?
as a follow up question. should I change my "stoich afr" table in hp tuners to reflect e10 fuel?
09-15-2015, 02:32 PM
#10
Its not worth the trouble IMO. You figure all the millions of non flex fuel vehicles out there are running on tunes or carburetors setup for non ethanol fuel. Here the pumps also say up to 10% ethanol but according to my tahoe I usually average 2-3% ethanol where I normally get gas. Without checking the fuel each time changing to the tune for 10% ethanol could make it farther off than just leaving it for zero ethanol. Now if your 100% sure the fuel is always 10% then that's a little different.
09-15-2015, 03:53 PM
#11
Its not worth the trouble IMO. You figure all the millions of non flex fuel vehicles out there are running on tunes or carburetors setup for non ethanol fuel. Here the pumps also say up to 10% ethanol but according to my tahoe I usually average 2-3% ethanol where I normally get gas. Without checking the fuel each time changing to the tune for 10% ethanol could make it farther off than just leaving it for zero ethanol. Now if your 100% sure the fuel is always 10% then that's a little different.
09-15-2015, 04:22 PM
#12
Around here I see anywhere from 5% to 9% ethanol content using an actual sensor with regular pump gas. Changing your stoich to 14.1 for E10 is nothing more than a few percent skew in fueling so it really is just about meaningless in the grand scheme of things. Hell your fuel trims will change by that much during the course of the day with no other changes even on a stock car.
09-15-2015, 04:44 PM
#13
09-19-2015, 11:57 PM
#14
I looked into tuning for this a few years ago and decided not to bother based on the reasons given by LSX Power Tuning and Nic D above. The only thing magical about stoich is that catalytic converters function most efficiently there - something I presume most guys on this board aren't overly concerned with. Otherwise, engines can run richer or leaner in various circumstances for best performance and efficiency.
09-20-2015, 01:05 AM
#15
FormerVendor
Join Date: Feb 2015
Location: Indiana
Posts: 147
Likes: 0
Received 0 Likes
on
0 Posts
Pump gas AFR Recently had a customer send fuel out to a lab for testing to confirm AFR for a project they were working on. Sent multiple samples from different sources. Average stoichiometric AFR of E10 pump fuel was 13.8:1. Surprised me.
I'm just starting to get into tuning, and I'm reviewing my tune, my stoichemetric afr is set for 14.681. which I believe is correct for gasoline. but the 93 octane I use around here is 10% ethanol.
should I change the stoich value in my pcm to an afr that is a little more appropriate for the blended fuel? such as 14.1 ish?
should I change the stoich value in my pcm to an afr that is a little more appropriate for the blended fuel? such as 14.1 ish?
09-20-2015, 10:12 PM
#17
The infuriating thing about this is that when you set out to try to tune to make up the difference, it all depends on the batch of fuel you happen to have in your tank at that point. And next time you fill up it could be different. Your results might be good for your part of the country at a given time. But elsewhere at different times, who knows? You'd have to torture yourself to find stoich at any given moment, only to possibly change at the next, for a negligible performance benefit. Or so it seems to me.