what do these fuel trims mean?

hello all

 

i was hoping someone could shed some light on the data log i will attach to this post. The log is from my 2008 outback xt with 5EAT

 

mods are: cobb down pipe, cob intake with a custom tune

 

i'm concerned about the AF learning 1 B at 18.75 and the AF correction 1 in general

 

the log is my drive home from work...with some idle time at the beginning and end.

 

any insight would be greatly appreciated.

 

https://drive.google.com/file/d/1wS6IZ-fM_5Aevzm0ePcqfzP5dEIh6GiG/view?usp=sharing

Edited July 13, 2019 by arcsnsparks

I took a very quick peek at it and it appears that the AF correction is trying to bring the trims back to 'normal'. You want to add the AF learn and the AF correction values and see what the total is. If it is close to 0% (e.g +/-5%), then your AF learn will slowly get back to normal soon. If the total is out of whack, then you may have some vacuum leak somewhere, especially if the grand total is positive (i.e. ecu adding fuel due to lean condition resulting from unmetered air entering the combustion chamber).

I took a very quick peek at it and it appears that the AF correction is trying to bring the trims back to 'normal'. You want to add the AF learn and the AF correction values and see what the total is. If it is close to 0% (e.g +/-5%), then your AF learn will slowly get back to normal soon. If the total is out of whack, then you may have some vacuum leak somewhere, especially if the grand total is positive (i.e. ecu adding fuel due to lean condition resulting from unmetered air entering the combustion chamber).

 

could a vacuum leak only affect the AF lerning 1 B

I took a very quick peek at it and it appears that the AF correction is trying to bring the trims back to 'normal'. You want to add the AF learn and the AF correction values and see what the total is. If it is close to 0% (e.g +/-5%), then your AF learn will slowly get back to normal soon. If the total is out of whack, then you may have some vacuum leak somewhere, especially if the grand total is positive (i.e. ecu adding fuel due to lean condition resulting from unmetered air entering the combustion chamber).

 

would a vacuum leak only affect AF learning 1 B

There are four 'AF learn values'. Each value refers to an amount of learned fuel correction for a specific air flow range. Quoting from this thread:

AF Learning #1 A: 0-5 grams per second. This is idle.

 

AF Learning #1 B: 5-10 g/s. A little more than idle, but so low it's difficult to reach with the car in gear.[2]

 

AF Learning #1 C: 10-40 g/s. This covers most of your cruising.

 

AF Learning #1 D: 40+ g/s. This is light acceleration, or cruising uphill. There is no strict upper bound for this range, but again the switch to open loop tends to happen around 60 g/s.

 

 

To answer your question, I'd doubt it. A vacuum leak would affect all fuel trims. It's just that it may be more apparent in a certain range of air flow depending on how small or large the vacuum leak is.

 

 

 

How were your learned values before you noticed this?

near 0 in A. +7ish at B. +3ish at C and -7ish at D.

 

the only change was B went from +7 to +18.75 and has stayed there for a few weeks now

 

i would get some increases in the B range ( 10 to 15)when i would drive the care over a mountain pass. the increase would happen on the decent. then the B range would relearn back to the typical number

 

the increase happend on my drive home a 3 weeks back and hasnot changed. i did refalsh the tune a but the 18.75 came back

Were these the values you had right after you got initially tuned? Cause after a proper tune, your values should be within +/-5%.

after the initial tune. the trims were positive across the board. near zero at idle. increasing steadily through the MAF ranges. max value i saw was +8 average 5 to 6 in Learning 1 D.

 

the tune has had a revision a few months back. after reviewing the logs i was told "this is as close as i can get it with out having it at the shop"

 

 

the reason for the revision was due to an modification i made to the intake. the tune shop that put on the cobb intake had the MAF sensor facing down and it was also pressed into the air box hard enough to cut into the plastic housing of the MAF itself. also the cone filter was pushed against the inside of the fender well and distorting and wrinkling the filter. so i trimmed the MAF housing half an inch to give the air filter some room and re worked the mounting bracket for the filter and MAF housing so the MAF sensor was accessible without taking the intake apart.