Question for those with a tune
And that screws with your dyno numbers too, they will lower after you re-dyno. Post graphs.
You have the option to disable LTFT and just use STFT. If the tune is close enough, you don't need the LTFT and don't need to worry about them locking in during PE and messing up your WOT fueling.
The only other learn function that I'm aware of is knock learn - the more knock that is detected, the more timing moves closer to the low octane timing table values. When knock disappears, timing moves back towards the high octane table values, but it takes longer to "unlearn" knock adjustments with the stock settings.
TECH Enthusiast
Joined: Nov 2008
Posts: 622
Likes: 1
"I'm going to disagree with this statement. At least with HPT, LT fuel trims do not reset with a flash, you have to do that separately. The fuel trims will adjust after ~75 miles."
It is not the LTFT that is reset (unless you tell them), It is the memory/learn which comes from the activity of the STFT`s. So everytime you reflash the PCM/ECM the previous memory is lost/erased.
What ever LTFT # in the basic tune info (is not locked in during PE mode/ open loop) it is only referenced/ used during closed loop mode.
As for relearn , there are many variables and systems for relearn.
Fuel trims,AIS, Idle, MAF,IAT,MAP,KR, Driver input,Fuel SG, the list goes on and then there is the tranny side to. Oh yes there is also the 17hr cycle of the computer and many many more little hidden secrets.
It is not the LTFT that is reset (unless you tell them), It is the memory/learn which comes from the activity of the STFT`s. So everytime you reflash the PCM/ECM the previous memory is lost/erased.
What ever LTFT # in the basic tune info (is not locked in during PE mode/ open loop) it is only referenced/ used during closed loop mode.
As for relearn , there are many variables and systems for relearn.
Fuel trims,AIS, Idle, MAF,IAT,MAP,KR, Driver input,Fuel SG, the list goes on and then there is the tranny side to. Oh yes there is also the 17hr cycle of the computer and many many more little hidden secrets.
Staging Lane
Joined: Jul 2009
Posts: 72
Likes: 0
Then again maybe its like your radio presets - each time you disconnect the battery this information is lost and you start over.
I'm guessing here - looking for clarification about how this works.
TECH Enthusiast
Joined: Nov 2008
Posts: 622
Likes: 1
Under normal conditions, STFT is what
keeps the engine near the best overall air-fuel
ratio of 14.7:1 (stoichiometric). STFT
values are retained in the PCM’s volatile
memory and are erased as soon as the ignition
key is switched OFF. These values “start from
scratch” each time the engine is restarted.
LTFT is a learned value that is determined
by trends in short term fuel correction.
LTFT values are stored in the PCM’s
Keep Alive Memory (KAM) and stay there
unless they are reset with a scan tool or erased
when the PCM’s power source is disconnected or reflashed
(unless you actually save your changes)
This also erases the PCM’s long term fuel correction
information, allowing it to start fresh.
The PCM constantly monitors both
STFT and LTFT to determine if the
fuel system is operating normally. If
STFT goes beyond its limit in an attempt
to control the mixture, LTFT will also
be affected. If STFT correction
continues, LTFT will experience a major
change. Both STFT and LTFT can
compensate for a rich or lean condition, but
they can only take it so far.
keeps the engine near the best overall air-fuel
ratio of 14.7:1 (stoichiometric). STFT
values are retained in the PCM’s volatile
memory and are erased as soon as the ignition
key is switched OFF. These values “start from
scratch” each time the engine is restarted.
LTFT is a learned value that is determined
by trends in short term fuel correction.
LTFT values are stored in the PCM’s
Keep Alive Memory (KAM) and stay there
unless they are reset with a scan tool or erased
when the PCM’s power source is disconnected or reflashed
(unless you actually save your changes)
This also erases the PCM’s long term fuel correction
information, allowing it to start fresh.
The PCM constantly monitors both
STFT and LTFT to determine if the
fuel system is operating normally. If
STFT goes beyond its limit in an attempt
to control the mixture, LTFT will also
be affected. If STFT correction
continues, LTFT will experience a major
change. Both STFT and LTFT can
compensate for a rich or lean condition, but
they can only take it so far.
