Please explain the relation between ltft's and stft's and why they affect WOT fuel.
05-31-2004, 02:44 PM
#1
TECH Junkie
Thread Starter
Join Date: Dec 2001
Location: Lakeland, FL
Posts: 3,242
Likes: 0
Received 0 Likes
on
0 Posts
Please explain the relation between ltft's and stft's and why they affect WOT fuel. I have run a search but found nothing really about the short term fuel trims as opposed to the long term fuel trims. I know that the long term fuel trims should be in the negative meaning the PCM thinks you are rich at part throttle and will not give the extra fuel upon WOT. If this is the case what are the short term fuel trims for and what relation do they have to the long term fuel trims?
Also when at WOT doesn't the PCM use closed loop operation which bypasses the o2's input anyways?
If all this is true then why would stfts or ltfts mean anything at all other than for part throttle driving? I guess I can see the use of the o2 sensor for collecting data even if it is not being used at WOT to give a general basis for the a/f ratio but I am curious as to how all this ties together. Any input would be great.
Also when at WOT doesn't the PCM use closed loop operation which bypasses the o2's input anyways?
If all this is true then why would stfts or ltfts mean anything at all other than for part throttle driving? I guess I can see the use of the o2 sensor for collecting data even if it is not being used at WOT to give a general basis for the a/f ratio but I am curious as to how all this ties together. Any input would be great.
05-31-2004, 10:38 PM
#2
TECH Fanatic
iTrader: (12)
Join Date: May 2004
Location: Elgin, Illinois
Posts: 1,080
Likes: 0
Received 0 Likes
on
0 Posts
id like to know more about this too, but i thnk it looks at the last part throttle FTC it was in and if its negative it does not add fuel. If its positive it will.
dave
dave
05-31-2004, 10:52 PM
#3
TECH Junkie
Thread Starter
Join Date: Dec 2001
Location: Lakeland, FL
Posts: 3,242
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by TT_Vert
id like to know more about this too, but i thnk it looks at the last part throttle FTC it was in and if its negative it does not add fuel. If its positive it will.
dave
dave
Does the PCM re write its WOT values according to data gathered by the o2's during previous runs?
06-01-2004, 12:14 AM
#4
TECH Resident
Join Date: Jan 2002
Location: USA
Posts: 754
Likes: 0
Received 0 Likes
on
0 Posts
IMHO This is all misunderstood.
The engine functions off the SHORT (realtime) term fuel trims after engine has warmed up and PCM goes into closed loop. It's data is erased when the engine is turned off.
It has an operating window of -10% to +10%, IF the values exceed that for more then 15 seconds the PCM bumps up the LONG term fuel trims values.
As long as STFT is within its window, LTFT is ignored.
LTFT as it is called is to correct trims over a long period of time, not realtime.
It's values are saved in protected memory and get cleared only if power is removed.
It's purpose is for a long term correction as engine and sensors degrade over time or to
clean up a condition such as a very long lean idle that over some minutes caused LTFT values to increase.
When TPS signals to go into PE and other sensors are also reporting a PE state under EPA rules PE is not part of smog rules so to protect their fuel trim values, when PCM switches to PE mode the STFT is cleared to ZERO and is frozen so while in the richer PE state the LTFTs are not being used or can the rich AFR effect the LTFT averages
so when returning from a PE state the LTFTs are where they were before going into PE
The PCM ONLY reacts to LTFTs once every 10 minutes since it is a long term correction factor.
PCM uses STFT and O2s for realtime AFR adjustment which is a fine tune AFR change, it will not do large changes in realtime for engine would never run smooth as example pulling up a steep hill, the top of the hill and then going down the hill, so large change would cause engine to buck around.
EPA requires a rich DTC to trigger if LTFT reaches -13% and lean DTC if exceeds +22.
IF EPA trim cells are close to within STFT window then no matter if its a bit rich or lean should have no effect on PE IF the PE tables are tuned correctly meaning, some people have their PE tables incorrect and if the EPA trim average is a bit rich or lean then as going into PE they would have an effect to PE but as long as you properly tune EPA cells and then tune PE table then EPA cells should have no effect on PE.
As soon as PE enters PE state then Fuel Learn is turned OFF which tells PCM to ignore the O2s, thus since STFTs use them then they also are forced to zero so being LTFTs are frozen during PE they should have no effect on PE.
When in EPA cells and O2s are being read by PCM ( fuel learn is now ON) it does so only once a second for their purpose is only to assure the overall AFR of 14.7:1 long term is met but as can be seen the PCM can run as much as 13% too rich or +22 lean which is within the FTP of being no more then 1 1/2 times of EPA requirement.
I do not go by the cyberspace rule of LTFTs being biased rich, I have tuned EPA cells to be on the lean side, tuned PE and then had zero effect on PE as to what the EPA cells average was being engine runs off of STFTs and being they are forced to zero when in PE then clearly it should not be adding or subtracting to the commanded AFR the PE table does.
LTFT defined :
Long Term Fuel Trim Description
The long term fuel trim (FT) is a matrix of cells arranged by RPM and MAP. Each cell of the long term FT is a register like the short term FT. As the engine operating conditions change, the PCM will switch from cell to cell to determine what long term FT factor to use in the base pulse width equation.
While in any given cell, the PCM also monitors the short term FT. If the short term FT is far enough from 0 percent, the PCM will change the long term FT value. Once the long term FT value is changed, it should force the short term FT back toward 0 percent. If the mixture is still not correct (as judged by the PCM), the short term FT will continue to have a large deviation from the ideal 0 percent. In this case, the long term FT value will continue to change until the short term FT becomes balanced. Both the short term FT and long term FT have limits which vary by calibration. If the mixture is off enough so that long term FT reaches the limit of its control and still cannot correct the condition, the short term FT would also go to its limit of control in the same direction. If the mixture is still not corrected by both short term FT and long term FT at their extreme values, a FT DTC will likely result. When the PCM determines that the long term FT is out of the operating range, the following DTCs will set:
DTC P0171 FT System Lean Bank 1
DTC P0172 FT System Rich Bank 1
DTC P0174 FT System Lean Bank 2
DTC P0175 FT System Rich Bank 2
Under the conditions of power enrichment, the PCM sets the short term FT to 0 percent and freezes it there until power enrichment is no longer in effect.
This is done so the Closed Loop factor and the long term FT will not try to correct for the commanded richness of power enrichment.
The engine functions off the SHORT (realtime) term fuel trims after engine has warmed up and PCM goes into closed loop. It's data is erased when the engine is turned off.
It has an operating window of -10% to +10%, IF the values exceed that for more then 15 seconds the PCM bumps up the LONG term fuel trims values.
As long as STFT is within its window, LTFT is ignored.
LTFT as it is called is to correct trims over a long period of time, not realtime.
It's values are saved in protected memory and get cleared only if power is removed.
It's purpose is for a long term correction as engine and sensors degrade over time or to
clean up a condition such as a very long lean idle that over some minutes caused LTFT values to increase.
When TPS signals to go into PE and other sensors are also reporting a PE state under EPA rules PE is not part of smog rules so to protect their fuel trim values, when PCM switches to PE mode the STFT is cleared to ZERO and is frozen so while in the richer PE state the LTFTs are not being used or can the rich AFR effect the LTFT averages
so when returning from a PE state the LTFTs are where they were before going into PE
The PCM ONLY reacts to LTFTs once every 10 minutes since it is a long term correction factor.
PCM uses STFT and O2s for realtime AFR adjustment which is a fine tune AFR change, it will not do large changes in realtime for engine would never run smooth as example pulling up a steep hill, the top of the hill and then going down the hill, so large change would cause engine to buck around.
EPA requires a rich DTC to trigger if LTFT reaches -13% and lean DTC if exceeds +22.
IF EPA trim cells are close to within STFT window then no matter if its a bit rich or lean should have no effect on PE IF the PE tables are tuned correctly meaning, some people have their PE tables incorrect and if the EPA trim average is a bit rich or lean then as going into PE they would have an effect to PE but as long as you properly tune EPA cells and then tune PE table then EPA cells should have no effect on PE.
As soon as PE enters PE state then Fuel Learn is turned OFF which tells PCM to ignore the O2s, thus since STFTs use them then they also are forced to zero so being LTFTs are frozen during PE they should have no effect on PE.
When in EPA cells and O2s are being read by PCM ( fuel learn is now ON) it does so only once a second for their purpose is only to assure the overall AFR of 14.7:1 long term is met but as can be seen the PCM can run as much as 13% too rich or +22 lean which is within the FTP of being no more then 1 1/2 times of EPA requirement.
I do not go by the cyberspace rule of LTFTs being biased rich, I have tuned EPA cells to be on the lean side, tuned PE and then had zero effect on PE as to what the EPA cells average was being engine runs off of STFTs and being they are forced to zero when in PE then clearly it should not be adding or subtracting to the commanded AFR the PE table does.
LTFT defined :
Long Term Fuel Trim Description
The long term fuel trim (FT) is a matrix of cells arranged by RPM and MAP. Each cell of the long term FT is a register like the short term FT. As the engine operating conditions change, the PCM will switch from cell to cell to determine what long term FT factor to use in the base pulse width equation.
While in any given cell, the PCM also monitors the short term FT. If the short term FT is far enough from 0 percent, the PCM will change the long term FT value. Once the long term FT value is changed, it should force the short term FT back toward 0 percent. If the mixture is still not correct (as judged by the PCM), the short term FT will continue to have a large deviation from the ideal 0 percent. In this case, the long term FT value will continue to change until the short term FT becomes balanced. Both the short term FT and long term FT have limits which vary by calibration. If the mixture is off enough so that long term FT reaches the limit of its control and still cannot correct the condition, the short term FT would also go to its limit of control in the same direction. If the mixture is still not corrected by both short term FT and long term FT at their extreme values, a FT DTC will likely result. When the PCM determines that the long term FT is out of the operating range, the following DTCs will set:
DTC P0171 FT System Lean Bank 1
DTC P0172 FT System Rich Bank 1
DTC P0174 FT System Lean Bank 2
DTC P0175 FT System Rich Bank 2
Under the conditions of power enrichment, the PCM sets the short term FT to 0 percent and freezes it there until power enrichment is no longer in effect.
This is done so the Closed Loop factor and the long term FT will not try to correct for the commanded richness of power enrichment.
Last edited by Team ZR-1; 06-01-2004 at 12:19 AM.
06-01-2004, 09:22 AM
#5
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
Your explanation is confusingly worded. When you say
that LTFT values are "ignored as long as STFT is in
its window", that doesn't mean that LTFT is absent
in the real-time fuel shot computation? Only that the
STFT does not increment / decrement the LTFT value.
The advice to get negative cells is purely to get WOT
baseline consistency (by <=0.0 LTFT). What is the
performance penalty for being "trimmed right" vs being
"tuned right"? Conversely, if you are picking up a comes-
and-goes percent of WOT enrichment from LTFT drift
"over the line" in a cell or two, do you just tolerate it
by being trued-up to peak power mixture at WOT (with
that also having minimum power/AFR local sensitivity?
that LTFT values are "ignored as long as STFT is in
its window", that doesn't mean that LTFT is absent
in the real-time fuel shot computation? Only that the
STFT does not increment / decrement the LTFT value.
The advice to get negative cells is purely to get WOT
baseline consistency (by <=0.0 LTFT). What is the
performance penalty for being "trimmed right" vs being
"tuned right"? Conversely, if you are picking up a comes-
and-goes percent of WOT enrichment from LTFT drift
"over the line" in a cell or two, do you just tolerate it
by being trued-up to peak power mixture at WOT (with
that also having minimum power/AFR local sensitivity?
Trending Topics
09-02-2004, 02:44 PM
#8
Moderator
I wanted to review fine-tuning Cells because I'd changed my fuel pressure and did a search on Fuel Trim Cells.
I've seen Team ZR-1 try to address this issue of LTFT's and our tendency to try to make them zero to slightly negative a number of times and either I've misread what he has said before, or the following part has never been quite clear before in all the detail/verbage:
Let me make a few concise statements based on what I understand from this piece and what some of us at trying to do:
1. The goal is to take out any adjustments to AFR, other than the PE table values, to ease tuning.
2. Contrary to what many of us think, Team ZR-1 is saying STFT's (NOT LTFT's) is what adds or subtracts fuel in addition to the PE tables, if the tune is off enough (i.e., certain cells are whack).
3. Conclusion: If STFT's are zeroed during WOT, you are done.
Question: If we are close to zero STFT's during WOT, rather than hacking broadly at the whole MAF table or the whole IFR table, is it true that some adjustments of the
?MAF table in freqs?
or
?Fuel Air Multiplier table?
or
?VE table?
that coincide with the FTC's Team ZR-1 refers to may be enough to do the trick? Then, forget about chasing LTFT's throughout the year?
Help me understand on this one. Are you still out there, Team ZR-1?
Thanks, guys, for yet more discussion on this topic.
I've seen Team ZR-1 try to address this issue of LTFT's and our tendency to try to make them zero to slightly negative a number of times and either I've misread what he has said before, or the following part has never been quite clear before in all the detail/verbage:
Originally Posted by Team ZR-1
...
I do not go by the cyberspace rule of LTFTs being biased rich, I have tuned EPA cells to be on the lean side, tuned PE and then had zero effect on PE as to what the EPA cells average was being engine runs off of STFTs and being they are forced to zero when in PE then clearly it should not be adding or subtracting to the commanded AFR the PE table does.
...
[/b]
I do not go by the cyberspace rule of LTFTs being biased rich, I have tuned EPA cells to be on the lean side, tuned PE and then had zero effect on PE as to what the EPA cells average was being engine runs off of STFTs and being they are forced to zero when in PE then clearly it should not be adding or subtracting to the commanded AFR the PE table does.
...
[/b]
1. The goal is to take out any adjustments to AFR, other than the PE table values, to ease tuning.
2. Contrary to what many of us think, Team ZR-1 is saying STFT's (NOT LTFT's) is what adds or subtracts fuel in addition to the PE tables, if the tune is off enough (i.e., certain cells are whack).
3. Conclusion: If STFT's are zeroed during WOT, you are done.
Question: If we are close to zero STFT's during WOT, rather than hacking broadly at the whole MAF table or the whole IFR table, is it true that some adjustments of the
?MAF table in freqs?
or
?Fuel Air Multiplier table?
or
?VE table?
that coincide with the FTC's Team ZR-1 refers to may be enough to do the trick? Then, forget about chasing LTFT's throughout the year?
Help me understand on this one. Are you still out there, Team ZR-1?
Thanks, guys, for yet more discussion on this topic.
Last edited by Black LS1 T/A; 09-02-2004 at 03:55 PM.
09-02-2004, 04:06 PM
#9
Moderator
Here's a current log where I'm knocking down KR on pump gas by adjusting the fuel and was whittling my way back down to zero/neg on LTFT's.
http://www.blackls1ta.com/Log2004-09-02.htm
LTFT's are close, but STFT is already there.
http://www.blackls1ta.com/Log2004-09-02.htm
LTFT's are close, but STFT is already there.
09-02-2004, 04:08 PM
#10
Moderator
I also struggle with the decision as to whether this '98 is exhibiting false knock or KR induced by noises other than being too lean. I'll get some 100 octane in a bit, so I can try to eliminate some of that factor.
09-02-2004, 04:12 PM
#11
12 Second Truck Club
iTrader: (1)
Join Date: Jun 2004
Location: The Chicken Ranch, California
Posts: 1,395
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Black LS1 T/A
Here's a current log where I'm knocking down KR on pump gas by adjusting the fuel and was whittling my way back down to zero/neg on LTFT's.
http://www.blackls1ta.com/Log2004-09-02.htm
LTFT's are close, but STFT is already there.
http://www.blackls1ta.com/Log2004-09-02.htm
LTFT's are close, but STFT is already there.
09-02-2004, 06:31 PM
#12
here is a page i wrote on hptuners, it explains a little bit about ve and ltrims ect..
http://www.hptuners.com/forum/YaBB.p...0521;start=3#3
and ltrims and strims work off of that ve table, so ltrims are the amount that the pcm is away from 14.7 af. and short terms are just a breif amount away, if they go to high or low, then they instantly change the ltrim to make up for it, so if you have a 1 ltrim and a 5 strim then actually at that given time you are actually 6 % off, not just the 1. or the 5.. ltrims are used at wot not strims and ltrims are different for every cell.. that is how the pcm corrects for fueling to keep the wot fuel in line. and make all the other pcm equations close and more accurate "pe vs rpm" ect. thanks jes
http://www.hptuners.com/forum/YaBB.p...0521;start=3#3
and ltrims and strims work off of that ve table, so ltrims are the amount that the pcm is away from 14.7 af. and short terms are just a breif amount away, if they go to high or low, then they instantly change the ltrim to make up for it, so if you have a 1 ltrim and a 5 strim then actually at that given time you are actually 6 % off, not just the 1. or the 5.. ltrims are used at wot not strims and ltrims are different for every cell.. that is how the pcm corrects for fueling to keep the wot fuel in line. and make all the other pcm equations close and more accurate "pe vs rpm" ect. thanks jes
09-03-2004, 12:12 PM
#13
Moderator
Originally Posted by Magic Chicken
That's a nice log, what do you use for the logging? I noticed the HP and TQ numbers, that's the main reason I ask.
I use a VB app I wrote to organize and color-code the columns so it is easy to read between runs at the track. Thanks!
The TQ is derived from the PCM (based on MAF and other calcs I guess) , and I derive HP from a formula using torque. It's not precise. But, it does happen to be true that my highest RWHP on the dyno was 549.
09-03-2004, 12:44 PM
#14
Moderator
Originally Posted by wait4me
here is a page i wrote on hptuners, it explains a little bit about ve and ltrims ect..
http://www.hptuners.com/forum/YaBB.p...0521;start=3#3
and ltrims and strims work off of that ve table, so ltrims are the amount that the pcm is away from 14.7 af. and short terms are just a breif amount away, if they go to high or low, then they instantly change the ltrim to make up for it, so if you have a 1 ltrim and a 5 strim then actually at that given time you are actually 6 % off, not just the 1. or the 5.. ltrims are used at wot not strims and ltrims are different for every cell.. that is how the pcm corrects for fueling to keep the wot fuel in line. and make all the other pcm equations close and more accurate "pe vs rpm" ect. thanks jes
http://www.hptuners.com/forum/YaBB.p...0521;start=3#3
and ltrims and strims work off of that ve table, so ltrims are the amount that the pcm is away from 14.7 af. and short terms are just a breif amount away, if they go to high or low, then they instantly change the ltrim to make up for it, so if you have a 1 ltrim and a 5 strim then actually at that given time you are actually 6 % off, not just the 1. or the 5.. ltrims are used at wot not strims and ltrims are different for every cell.. that is how the pcm corrects for fueling to keep the wot fuel in line. and make all the other pcm equations close and more accurate "pe vs rpm" ect. thanks jes
There are such hugely divergent opinions on this stuff.
Have you written anything on your approach to tuning with the VE? I'll go back and review that VE thread stickied in this forum.
09-03-2004, 12:53 PM
#15
TECH Senior Member
Originally Posted by wait4me
here is a page i wrote on hptuners, it explains a little bit about ve and ltrims ect..
http://www.hptuners.com/forum/YaBB.p...0521;start=3#3
and ltrims and strims work off of that ve table, so ltrims are the amount that the pcm is away from 14.7 af. and short terms are just a breif amount away, if they go to high or low, then they instantly change the ltrim to make up for it, so if you have a 1 ltrim and a 5 strim then actually at that given time you are actually 6 % off, not just the 1. or the 5.. ltrims are used at wot not strims and ltrims are different for every cell.. that is how the pcm corrects for fueling to keep the wot fuel in line. and make all the other pcm equations close and more accurate "pe vs rpm" ect. thanks jes
http://www.hptuners.com/forum/YaBB.p...0521;start=3#3
and ltrims and strims work off of that ve table, so ltrims are the amount that the pcm is away from 14.7 af. and short terms are just a breif amount away, if they go to high or low, then they instantly change the ltrim to make up for it, so if you have a 1 ltrim and a 5 strim then actually at that given time you are actually 6 % off, not just the 1. or the 5.. ltrims are used at wot not strims and ltrims are different for every cell.. that is how the pcm corrects for fueling to keep the wot fuel in line. and make all the other pcm equations close and more accurate "pe vs rpm" ect. thanks jes
09-04-2004, 05:09 PM
#17
TECH Addict
Join Date: Sep 2003
Location: Atlanta, GA
Posts: 2,065
Likes: 0
Received 0 Likes
on
0 Posts
monitor injector duty cycle at wot, cause after the injectors go static (stockers usually do with cam/boltons) it really wont make a bit of a different if you run them injectors static. laws of physics here. injectors go static long before 100 
i see mine hit 100% way before peak whp on my tune.
obviously 101% is meaningless since injectors only go 0-100% and somewhere around 85% they like to jump static (depending on injector make etc)
i see mine hit 100% way before peak whp on my tune.obviously 101% is meaningless since injectors only go 0-100% and somewhere around 85% they like to jump static (depending on injector make etc)
09-07-2004, 12:35 AM
#18
Wait4me, i have a question. How does the cell 22 ltft get calculated? Does it just take the value of the ltft of the last ftc you were in when you transitioned to w.o.t.?
Nevermind, I just read that post you linked to. So am I understanding this right? If ftc 15 has a ltft of +5 stored in it, and my pe enrichment is 1.24 at whatever rpm i'm at, then my ltft in cell 22 will be +29?
Nevermind, I just read that post you linked to. So am I understanding this right? If ftc 15 has a ltft of +5 stored in it, and my pe enrichment is 1.24 at whatever rpm i'm at, then my ltft in cell 22 will be +29?
09-13-2004, 07:24 AM
#19
sorry i didnt see that anyone added anything,
cell 22, is powerenrichment mode, so what is going on is.. the computer sees the requirements needed to go into the mode, it takes the ltrims from the current cell it was in as it entered pe mode, and adds that value all the way thru untill it goes out of pe mode..
the reason it took the ltrim of that cell is because the computer assumes that since it was lean in that cell it will be lean durring wot, so it adds that amount,
lets say you are at 4000 rpm, and that cell has +4 ltrims and +2 strims, at that time it is actually +6 % too rich, so the computer is adding 6% more fuel to the ve table equation to equal a 14.7 a.f. now, when the computer is done storing all the ltrim data for all cells, the whole table will be 14.7, and all the pe and other calculations "open loop f/a " should be right on.. 14.7 / the number in pe, equals the desired a/f ratio.
Our stock o2 sensors are very accurate at 14.7, thats why for years now, ive been telling people that we can let our computers tell us how it needs to be set up.. the ve table, and all the other important tables.
Real world observation and logging/ driving in my oppinion is much better than a long complicated mathmatical calculation to try and come up with something like this, its very easy to not have all the variables needed to get the correct results, "everyone thinks thiers are right"
Just a hint for people that want to set up the ve table, you need to disconnect your maf. and drive it in speed density, set up the fuel cell boundry table to be higher resolution in the area you are working in, fill in your results from the percentage of ltrims you are seeing, , then change the cell boundry again untill you are all done and you have a "computer assisted" ve table and will "if you do it right" a complete 0 ltrim everywhere, and a + - strim usually around 5, and normally doesnt take two hours of driving.
and after doing this, you are able to hit within a .2 on your desired af ratio you want, like if you say you want a 12.7 at wot, it is within that range, either a 12.8 a 12.7 or a 12.6 ...
the computer shows us what it needs, we just have to insert that data.
so much to say, not enough time.....
cell 22, is powerenrichment mode, so what is going on is.. the computer sees the requirements needed to go into the mode, it takes the ltrims from the current cell it was in as it entered pe mode, and adds that value all the way thru untill it goes out of pe mode..
the reason it took the ltrim of that cell is because the computer assumes that since it was lean in that cell it will be lean durring wot, so it adds that amount,
lets say you are at 4000 rpm, and that cell has +4 ltrims and +2 strims, at that time it is actually +6 % too rich, so the computer is adding 6% more fuel to the ve table equation to equal a 14.7 a.f. now, when the computer is done storing all the ltrim data for all cells, the whole table will be 14.7, and all the pe and other calculations "open loop f/a " should be right on.. 14.7 / the number in pe, equals the desired a/f ratio.
Our stock o2 sensors are very accurate at 14.7, thats why for years now, ive been telling people that we can let our computers tell us how it needs to be set up.. the ve table, and all the other important tables.
Real world observation and logging/ driving in my oppinion is much better than a long complicated mathmatical calculation to try and come up with something like this, its very easy to not have all the variables needed to get the correct results, "everyone thinks thiers are right"
Just a hint for people that want to set up the ve table, you need to disconnect your maf. and drive it in speed density, set up the fuel cell boundry table to be higher resolution in the area you are working in, fill in your results from the percentage of ltrims you are seeing, , then change the cell boundry again untill you are all done and you have a "computer assisted" ve table and will "if you do it right" a complete 0 ltrim everywhere, and a + - strim usually around 5, and normally doesnt take two hours of driving.
and after doing this, you are able to hit within a .2 on your desired af ratio you want, like if you say you want a 12.7 at wot, it is within that range, either a 12.8 a 12.7 or a 12.6 ...
the computer shows us what it needs, we just have to insert that data.
so much to say, not enough time.....
