True tuning expertise?
01-06-2010, 08:40 AM
#21
Another point to hit on is a good tuners ability to pick up on and solve problems as they come along. Knowing when to put the computer away and trouble shoot actual problems instead of "tuning around them".
As we all know when making a lot of changes to a car all at once problems can arise.
As we all know when making a lot of changes to a car all at once problems can arise.
01-06-2010, 08:58 AM
#22
There are many ways to control fueling, MAF, PE, VE, MAP, IFR and a combination of all. Ask this and you will get a ton of answers to why use what. If you use any of the above and your fueling stays constant thru cruise and wot then is that the wrong way to do it? and if so, who is to say its wrong.
If the tables you mentioned only affected fuel, and adjusting them would allow you to get the car to stop self adjusting itself out of range...then yes I'd tend to agree more.
However, those tables, are used to determine airflow, and airflow determines both fuel and spark...so tweaking the "wrong" table to get the fuel trims in line with a lot of engine mods, alters the airflow calculation, and changes spark advance...then you have to go after the spark advance tables, and suddenly there's no correlation between why it's running so much spark at any given airflow, because those airflow numbers aren't really whats happening.
LTFT are there for a reason, as are STFT, but if you notice, the cell matrix for them, is a significantly lower resolution than the tables they affect.
If some of the fuel trim cells are adding fuel, and others are subtracting, thats a sign to me, of an incomplete tune. If they're all in the same range, then thats a sign of a quality tune...probably just tuned with gas from a different pump or a different refinery. The LTFT shouldn't be used to say "well, it's only adding 5% here and only pulling 4% here...it's close enough", it should be there for the car to use as a correction for the fuel in the tank being different, or some other external change that the car can't properly correct for on the input side of things (like humidity...the car can measure air mass, but not water content on the way in). In this regard, the resolution of the matrix for the LTFT almost doesn't matter...if the fuel is different (different alcohol content that day, or different other additives) and the O2 sensor decides you need 8% more as a result at idle and light throttle than it needed a week ago with different gas in the tank...guess what...you'll probably need 8% more across the board...so in that case, I wouldn't worry about it, but I would try filling the car up at a different station, with a different brand of fuel on the next tank, and seeing where the fuel trims go with it.
The STFT is an excellent tool for a tuner to eventually nail down the VE table (not the entire table, but the parts of it where you're still in closed loop) and the lower frequencies of the MAF table...but it takes time too...it's a resolution issue again. As engine mods change the VE table...they change the overall shape of it...so where the airflow might be 10% different on one edge of the STFT cell, it might only be 4% different on another edge of that same cell...this makes it an iterative process to get that table tuned in and smoothed out. So in that regard, you can also use your STFT to see how smooth the tables are overall (both VE and MAF)...if you see them moving up and down as your MAP sensor changes a little bit, or your RPM changes a little bit...it probably means the tables aren't as clean as they could be...in reality, if those tables are clean and smooth and "right" for the engine, the LTFT should be doing the correcting for the outside variables that the car can't measure, and the STFT should be doing very very little (given the car has been driven a bit with th different fuel or humidity or whatever variable changed in order for the STFT to correct it first while the LTFT catches it and brings it back in line...once the LTFT has had time to do it's job though...)...and as WeathermanShawn pointed out, when those tables aren't smooth, and the fuel trims are changing a lot as a result (even if it's only the STFT changing a lot, and not enough to really throw the LTFT off), you will notice the car feeling more jerky/less smooth...the smoother you get the tables, the better the car will drive, not necessarilly in speed of throttle response, but in smoothness of response...you'll usually notice a benefit to MPG as well...if the O2 sensors aren't always tweaking the fueling, even ever so slightly, the system will tend to be more efficient.
Last edited by Mike454SS; 01-06-2010 at 09:06 AM.
01-06-2010, 01:15 PM
#23
I kinda agree, but I kinda disagree as well.
If the tables you mentioned only affected fuel, and adjusting them would allow you to get the car to stop self adjusting itself out of range...then yes I'd tend to agree more.
However, those tables, are used to determine airflow, and airflow determines both fuel and spark...so tweaking the "wrong" table to get the fuel trims in line with a lot of engine mods, alters the airflow calculation, and changes spark advance...then you have to go after the spark advance tables, and suddenly there's no correlation between why it's running so much spark at any given airflow, because those airflow numbers aren't really whats happening.
LTFT are there for a reason, as are STFT, but if you notice, the cell matrix for them, is a significantly lower resolution than the tables they affect.
If some of the fuel trim cells are adding fuel, and others are subtracting, thats a sign to me, of an incomplete tune. If they're all in the same range, then thats a sign of a quality tune...probably just tuned with gas from a different pump or a different refinery. The LTFT shouldn't be used to say "well, it's only adding 5% here and only pulling 4% here...it's close enough", it should be there for the car to use as a correction for the fuel in the tank being different, or some other external change that the car can't properly correct for on the input side of things (like humidity...the car can measure air mass, but not water content on the way in). In this regard, the resolution of the matrix for the LTFT almost doesn't matter...if the fuel is different (different alcohol content that day, or different other additives) and the O2 sensor decides you need 8% more as a result at idle and light throttle than it needed a week ago with different gas in the tank...guess what...you'll probably need 8% more across the board...so in that case, I wouldn't worry about it, but I would try filling the car up at a different station, with a different brand of fuel on the next tank, and seeing where the fuel trims go with it.
The STFT is an excellent tool for a tuner to eventually nail down the VE table (not the entire table, but the parts of it where you're still in closed loop) and the lower frequencies of the MAF table...but it takes time too...it's a resolution issue again. As engine mods change the VE table...they change the overall shape of it...so where the airflow might be 10% different on one edge of the STFT cell, it might only be 4% different on another edge of that same cell...this makes it an iterative process to get that table tuned in and smoothed out. So in that regard, you can also use your STFT to see how smooth the tables are overall (both VE and MAF)...if you see them moving up and down as your MAP sensor changes a little bit, or your RPM changes a little bit...it probably means the tables aren't as clean as they could be...in reality, if those tables are clean and smooth and "right" for the engine, the LTFT should be doing the correcting for the outside variables that the car can't measure, and the STFT should be doing very very little (given the car has been driven a bit with th different fuel or humidity or whatever variable changed in order for the STFT to correct it first while the LTFT catches it and brings it back in line...once the LTFT has had time to do it's job though...)...and as WeathermanShawn pointed out, when those tables aren't smooth, and the fuel trims are changing a lot as a result (even if it's only the STFT changing a lot, and not enough to really throw the LTFT off), you will notice the car feeling more jerky/less smooth...the smoother you get the tables, the better the car will drive, not necessarilly in speed of throttle response, but in smoothness of response...you'll usually notice a benefit to MPG as well...if the O2 sensors aren't always tweaking the fueling, even ever so slightly, the system will tend to be more efficient.
If the tables you mentioned only affected fuel, and adjusting them would allow you to get the car to stop self adjusting itself out of range...then yes I'd tend to agree more.
However, those tables, are used to determine airflow, and airflow determines both fuel and spark...so tweaking the "wrong" table to get the fuel trims in line with a lot of engine mods, alters the airflow calculation, and changes spark advance...then you have to go after the spark advance tables, and suddenly there's no correlation between why it's running so much spark at any given airflow, because those airflow numbers aren't really whats happening.
LTFT are there for a reason, as are STFT, but if you notice, the cell matrix for them, is a significantly lower resolution than the tables they affect.
If some of the fuel trim cells are adding fuel, and others are subtracting, thats a sign to me, of an incomplete tune. If they're all in the same range, then thats a sign of a quality tune...probably just tuned with gas from a different pump or a different refinery. The LTFT shouldn't be used to say "well, it's only adding 5% here and only pulling 4% here...it's close enough", it should be there for the car to use as a correction for the fuel in the tank being different, or some other external change that the car can't properly correct for on the input side of things (like humidity...the car can measure air mass, but not water content on the way in). In this regard, the resolution of the matrix for the LTFT almost doesn't matter...if the fuel is different (different alcohol content that day, or different other additives) and the O2 sensor decides you need 8% more as a result at idle and light throttle than it needed a week ago with different gas in the tank...guess what...you'll probably need 8% more across the board...so in that case, I wouldn't worry about it, but I would try filling the car up at a different station, with a different brand of fuel on the next tank, and seeing where the fuel trims go with it.
The STFT is an excellent tool for a tuner to eventually nail down the VE table (not the entire table, but the parts of it where you're still in closed loop) and the lower frequencies of the MAF table...but it takes time too...it's a resolution issue again. As engine mods change the VE table...they change the overall shape of it...so where the airflow might be 10% different on one edge of the STFT cell, it might only be 4% different on another edge of that same cell...this makes it an iterative process to get that table tuned in and smoothed out. So in that regard, you can also use your STFT to see how smooth the tables are overall (both VE and MAF)...if you see them moving up and down as your MAP sensor changes a little bit, or your RPM changes a little bit...it probably means the tables aren't as clean as they could be...in reality, if those tables are clean and smooth and "right" for the engine, the LTFT should be doing the correcting for the outside variables that the car can't measure, and the STFT should be doing very very little (given the car has been driven a bit with th different fuel or humidity or whatever variable changed in order for the STFT to correct it first while the LTFT catches it and brings it back in line...once the LTFT has had time to do it's job though...)...and as WeathermanShawn pointed out, when those tables aren't smooth, and the fuel trims are changing a lot as a result (even if it's only the STFT changing a lot, and not enough to really throw the LTFT off), you will notice the car feeling more jerky/less smooth...the smoother you get the tables, the better the car will drive, not necessarilly in speed of throttle response, but in smoothness of response...you'll usually notice a benefit to MPG as well...if the O2 sensors aren't always tweaking the fueling, even ever so slightly, the system will tend to be more efficient.
Yes you are correct, I did not want to get into everything I did, But on this particular motor with the LTFT at a slight Positive everything else was good, Spark, Cruise A/F, Tip In, WOT and the STFT were not searching for correction, why? I don't know, maybe the airflow of the sheet metal intake? My point is you just don't shoot for a number, like say set your LTFT to -5% then say its good...
