Where are LTFT data stored?
 

I'm trying to understand how long term fuel trims are applied when in OL condition and where the learned data is stored. When looking at LTFT in a log does anyone know which table is storing the data and what breakpoints will cause it to shift from one learned value to the next?


I've found two tables AF learning #1 Airflow Ranges A and AF learning #1 Airflow Ranges B.


The tables contain different breakpoints:


[Table2D]
A B C D E
1.60 5.0 12.0 20.0 60.0


[Table2D]
A B C D E
0.80 3.4 8.5 16.0 45.0


There was some discussion I found on a search of RR forums here regarding these two tables but there was never a consensus of which table actually stored to data that I could find.


Anyone have any information on which table stores the data and how it is applied. Or are there conditions that will cause the learned trims to be pulled from table A vs table B?


The only information I can find is in this thread here:
http://www.ft86club.com/forums/showthread.php?p=1706473

The ltft data is stored in RAM as its can change .and its cleared if you reset or reflash ecu as ecu is reset on flashing the ROM which is actually EEROM.

I dont claim to know how the exact learning occurrs but their are several bands of ltft that are storred related to maf flow rates. As you go through the rpm range maf flow changes and you move through the different maf flow rate bands and you will see the different ltft applied. These values will change as temperature,atmospheric pressure, fuel composition eg ethanol conrent, ect changes.

just note ltft is stored and applied reliative to maf flow rates not rpm or throttle position, its a continuous learning process

ltft is the ecus attempt to correct maf scaling errors and account for temperature air density pressure and fuel changes.

their is a bit more explaination in the MAF Scaling link below

if you use the VGI maf scaling utility it will sort all this out for you

I've wondered this and I think I've asked it before on here. The thing that throws me off is I've seen LTFT jump when MAF flow was the same but crossing RPM thresholds. On my previous car (STI) it was all just MAF flow rate based, independent of RPM. On the BRZ it seems it might be a function of more than just that - not sure if it's due to 2 injector sets, but it seems different.

I think that this might be the case. However I've only played with one set of learning ranges, ECUtek only has one which ties in with Romraider's A so B is new to me.

Someone could always test it out if they have access.

be very difficult to work out unless somone looked at the code.
but maybe the change was due to a new learnt value of ltft being stored rarther than a threshold range being crossed ?

Thanks for the responses guys. I guess it doesn't really matter, I'm not a programmer and just looking for the information using a search function was difficult for me. I was happy to be able to find out anything at all. I don't have the background or skillset to take it any further than this.


I'm just trying to learn about the ECU and how all the sensors and tables in the rom interact to make adjustments to fueling in a broader sense. Not that I ever hope to become some great tuner that knows everything there is, but I'd like to understand how to read the datalogs and why the ECU makes the adjustments it does. I certainly understand that there can be multiple data sources being polled and that when looking at a datalog I am only seeing the result of those changes. I'm just trying to understand why to fuel trim changes when it does within OL conditions and what triggers it to happen. Whether it is airflow, rpm, load AF reading, or some combination of all.


One thing is becoming readily apparent ,it is much more complicated than I imagined. There are some incredibly smart people on these forums and I'm not as smart as I thought I was.

have a look here
http://www.norcalmotorsports.org/use...gGuide-0_5.pdf

the more you look into it the more complex it gets :-) never ending learning curve ignore all the turbo stuff in that guide the brz ecu operates in a similar manner

www.romraider.com also has some good guides

but if you just scaling maf use VGI utility then look at wayno's tune guide for OFT tunes

@steve99, thanks. It was @Waynos guides, your helpful links and the gathering of all my logs to fine tune my OFT tune that led me to ask the question. I have been reading everything I can find to learn how this all interacts expecially the guides over on romraider. As always, thanks for sharing information and your helpful responses.