Fuel Trims
06-01-2010, 01:07 PM
#1
Fuel Trims
Is there a good place to get some info on fuel trims (long and short term)? How they work? How to reset them, etc?
Kinda of a newb question, I know, but a quick search didn't really show up anything
EDIT: Fuel trims are very useful for scaling MAF and seeing when your car is in open loop in datalogs.
When your car enters open loop STFT (short term fuel trim) becomes 0
Scale MAF by multiplying the flow rates by half your LTFT ...
EX: say your LTFT is 10%, then multiply the relevant area by 1.05 ....etc
Kinda of a newb question, I know, but a quick search didn't really show up anything
EDIT: Fuel trims are very useful for scaling MAF and seeing when your car is in open loop in datalogs.
When your car enters open loop STFT (short term fuel trim) becomes 0
Scale MAF by multiplying the flow rates by half your LTFT ...
EX: say your LTFT is 10%, then multiply the relevant area by 1.05 ....etc
Last edited by stinksause; 07-10-2010 at 10:45 PM.
06-04-2010, 09:37 PM
#2
www.autoshop101.com/forms/h44.pdf explains it and gives background information
07-10-2010, 04:03 PM
#7
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I have been data loggin with my accessport. I understand anything over +10 and - 10 should be corrected. I have a k&n typhoon intake and have seen up to 19 and down to -22. How do I get these values as close to zero as possible? I am new to this but I understand the concepts just not the steps to apply them. Any help would be appreciated.
07-10-2010, 06:22 PM
#11
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Also I have an 04 mt with black halo racing ignition kit with msd wires, k&n typhoon intake, and accesscobb stage 1 tune. So you get a better idea of what I have. Please understand this all new to me but I am trying my best to understand what's going on.
07-10-2010, 08:10 PM
#14
If you are within +-5% for your LTFT, it is ok ... where in the load/RPM range are you experiencing this? At idle? At Cruise? At WOT throtle pulls?
That is the first question you need to ask. Then you need to scale your MAF in the correct ranges accordingly
That is the first question you need to ask. Then you need to scale your MAF in the correct ranges accordingly
07-10-2010, 10:35 PM
#16
What is it at idle?
I am assuming its +4% and +8% ... then I would scale my MAF by multiplying it by 1.02 and 1.04 in the corresponding areas, reflash the map, drive for a week or so and then see what your new LTFT is .... dont forget to smooth after you change the MAF scaling tho
Anything below like +-5% is okay .... but if you wanna be **** about it, you can still scale it.
I am assuming its +4% and +8% ... then I would scale my MAF by multiplying it by 1.02 and 1.04 in the corresponding areas, reflash the map, drive for a week or so and then see what your new LTFT is .... dont forget to smooth after you change the MAF scaling tho
Anything below like +-5% is okay .... but if you wanna be **** about it, you can still scale it.
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07-11-2010, 10:39 AM
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Yes those number are +4 and +8%. But how do you get 1.02 and 1.04 and what numbers do I multiply them by? And what is smoothing? Sorry for all the questions but I have read a engine management system books but nothing tells you the process you take to make changes. And I have searched this site and found nothing. Just more info shared by people who know what they are doing.
07-11-2010, 11:42 AM
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I have seen one forum that says you should take the short term and long term add them together and use that number. And it says you shouldn't change the first 2 cells. I'm assuming those are .086 and .098 but i don't really know.
07-11-2010, 08:49 PM
#21
First two cells are pretty much your idle, and low rpm cruise ... stft gets converted into ltft over time ... so make smaller changes to be safer ... I would rather be safe and make two changes, than make one wrong one...
... right click and interpolate, that's smoothing
... right click and interpolate, that's smoothing
11-04-2010, 11:34 AM
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Noob fuel trim question. I noticed yesterday that my ltft is +15. This seems high, and I was curious if it means possible issues, or is it in the range that could be considered normal? I am running MM base tune currently.
11-04-2010, 11:49 AM
#23
Extraordinary Engineering
I recommend posting a data log file in the Cobb datalogs thread
11-04-2010, 12:11 PM
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Good suggestion DarkBrew. I will use that thread to try to learn what is "normal".
As for my initial concerns, it was another example of the old adage a little bit of knowledge is a dangerous thing. I thought ltft was relatively stable, but it varies more than I thought. I am over +10 at idle and coasting, but on the gas it is only +1. I guess that value is not as strange as I thought.
As for my initial concerns, it was another example of the old adage a little bit of knowledge is a dangerous thing. I thought ltft was relatively stable, but it varies more than I thought. I am over +10 at idle and coasting, but on the gas it is only +1. I guess that value is not as strange as I thought.
