Negative LTFTs needed after VE tuning? Best way?
07-23-2005, 11:13 AM
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Negative LTFTs needed after VE tuning? Best way? The procedures I've read for VE/SD tuning I've found say little to nothing about negative LTFTs. If the various procedures are followed, the trims should all end up at zero or roughly centered around zero (positive and negative).
Are negative LTFTs somehow not necessary anymore, or am I missing something? Where do you introduce the intentional error to keep them negative if that's needed?
Assuming for the moment that the place to force the LTFTs negative is the VE, do you first get it perfect, then apply a slight percentage offset to the whole table, or just try to estimate roughly where PE will kick in and only shift the stoich/closed loop entries (which seems like it would be hard to get quite right, especially through weather changes).
A fixed percentage offset in the whole VE seems like one easy way to do it. Since the percentage shift is known, it should be easy to scale/compensate the PE table accordingly to get the actual desired AFR in PE mode.
Alternately, the IFR table could be scaled (which is what I have now), which should be fairly easy to compensate for accurately and predictably in the PE.
Tweaking a properly-calibrated MAF to get negative trims also seems tricky to get right. I didn't have much luck the last time I tried it, but maybe I'm smarter now. Again, calibrating it accurately and then introducing a known error are two separate issues.
One way or the other, getting consistent negative trims has to mean intentionally introducing error SOMEwhere, and probably compensating in the PE. If the VE, MAF, and every other table is perfect in some arbitrary weather condition, the trims are certain to go positive at some point as the weather changes, which will in turn make WOT richer than intended.
Or, is everyone just dialing it in perfect, and then assuming that if trims go positive WOT probably NEEDs to go richer anyway? How do you tune that?
BTW, I'm using an LM-1 wideband. I understand how to get the tables RIGHT; what I'm unclear on is the best way to make them wrong
Are negative LTFTs somehow not necessary anymore, or am I missing something? Where do you introduce the intentional error to keep them negative if that's needed?
Assuming for the moment that the place to force the LTFTs negative is the VE, do you first get it perfect, then apply a slight percentage offset to the whole table, or just try to estimate roughly where PE will kick in and only shift the stoich/closed loop entries (which seems like it would be hard to get quite right, especially through weather changes).
A fixed percentage offset in the whole VE seems like one easy way to do it. Since the percentage shift is known, it should be easy to scale/compensate the PE table accordingly to get the actual desired AFR in PE mode.
Alternately, the IFR table could be scaled (which is what I have now), which should be fairly easy to compensate for accurately and predictably in the PE.
Tweaking a properly-calibrated MAF to get negative trims also seems tricky to get right. I didn't have much luck the last time I tried it, but maybe I'm smarter now. Again, calibrating it accurately and then introducing a known error are two separate issues.
One way or the other, getting consistent negative trims has to mean intentionally introducing error SOMEwhere, and probably compensating in the PE. If the VE, MAF, and every other table is perfect in some arbitrary weather condition, the trims are certain to go positive at some point as the weather changes, which will in turn make WOT richer than intended.
Or, is everyone just dialing it in perfect, and then assuming that if trims go positive WOT probably NEEDs to go richer anyway? How do you tune that?
BTW, I'm using an LM-1 wideband. I understand how to get the tables RIGHT; what I'm unclear on is the best way to make them wrong
07-24-2005, 07:25 AM
#2
From what I've read ( and take it for what it is, internet ) the original tuning doc may be inaccurate as it says +/-4.
Look for a post entitled 'opinions on ls1tuning doc' as there is some great discussion about this. Most tuners that gave an opinion felt they should be ALL negative but within 4 as ANY positive value will add fuel.
I have to say, I've been reading this and studying it all for months now and there is a TON of conflicting data, even WITHIN the tuning doc that is out there.
For example, the doc explains how to get to SD mode but others have said you also need to disable DFCO and PE so those 2 don't influence the VE table during the LTFT/STFT process. Not in the document; found it through hours of searching this board and HPTuners board.
BTW, been to Beaver Run lately? We met at a test and tune a couple of years ago with Sam Strano.
Look for a post entitled 'opinions on ls1tuning doc' as there is some great discussion about this. Most tuners that gave an opinion felt they should be ALL negative but within 4 as ANY positive value will add fuel.
I have to say, I've been reading this and studying it all for months now and there is a TON of conflicting data, even WITHIN the tuning doc that is out there.
For example, the doc explains how to get to SD mode but others have said you also need to disable DFCO and PE so those 2 don't influence the VE table during the LTFT/STFT process. Not in the document; found it through hours of searching this board and HPTuners board.
BTW, been to Beaver Run lately? We met at a test and tune a couple of years ago with Sam Strano.
07-24-2005, 09:44 AM
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I've been wondering the same thing. I'm pretty sure it's between the VE table and the MAF table. My theory of attacking this is to turn off your LTFT's & DFCO in SD and get your STFT's to average a slightly negative number. If you end up with cells that are more negative than say -2, I would apply only half of the percent correction. If you end up with cells that are positive, I would apply twice the correction. If it falls between -2 and 0, I would leave it be.
07-24-2005, 10:30 AM
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Originally Posted by Viper
"theory of attacking this is to turn off your LTFT's & DFCO in SD and get your STFT's to average a slightly negative number"
But, if your LTFT's are way over +/- 10, wouldn't you want to start with LTFT tuning first then move to STFT?
But, if your LTFT's are way over +/- 10, wouldn't you want to start with LTFT tuning first then move to STFT?
07-24-2005, 12:40 PM
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Originally Posted by Viper
BTW, been to Beaver Run lately? We met at a test and tune a couple of years ago with Sam Strano.
I did go to an Evolution in Cinci last year too, maybe we met then
07-24-2005, 12:57 PM
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The real problem is what could be considered a bug (actually a poor design choice) in the PCM firmware. One way or another, we have to introduce intentional error into at least one table to avoid the bug. That's what the trims are - learned compensation for errors in the tables.
I'm basically chasing the idea that any error introduced anywhere is going to have unintended side effects:
- Fudging the airflow tables will affect anything that uses calculated airflow (instead of MAP) to determine engine load and burn time. Notably, this includes the spark and knock calculations.
- Fudging the IFR probably throws off the transient fuel calculations.
- Fudging stoich (changing it from 14.62 to 14.0, for instance) would require compensating the Open Loop AFR table, but once that's done, I think a lot of things might just fall in line. Closed loop operation would still run at true stoich because that's where the sensors switch.
In other words, error has to be introduced somewhere and it will have side effects. The trick is to figure out which error(s) has/have the most benign side-effects to deal with.
I'm basically chasing the idea that any error introduced anywhere is going to have unintended side effects:
- Fudging the airflow tables will affect anything that uses calculated airflow (instead of MAP) to determine engine load and burn time. Notably, this includes the spark and knock calculations.
- Fudging the IFR probably throws off the transient fuel calculations.
- Fudging stoich (changing it from 14.62 to 14.0, for instance) would require compensating the Open Loop AFR table, but once that's done, I think a lot of things might just fall in line. Closed loop operation would still run at true stoich because that's where the sensors switch.
In other words, error has to be introduced somewhere and it will have side effects. The trick is to figure out which error(s) has/have the most benign side-effects to deal with.
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07-24-2005, 02:39 PM
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Originally Posted by Viper
Look for a post entitled 'opinions on ls1tuning doc' as there is some great discussion about this. Most tuners that gave an opinion felt they should be ALL negative but within 4 as ANY positive value will add fuel.
07-25-2005, 10:05 AM
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Originally Posted by sgarnett
The real problem is what could be considered a bug (actually a poor design choice) in the PCM firmware. One way or another, we have to introduce intentional error into at least one table to avoid the bug. That's what the trims are - learned compensation for errors in the tables.
I'm basically chasing the idea that any error introduced anywhere is going to have unintended side effects:
- Fudging the airflow tables will affect anything that uses calculated airflow (instead of MAP) to determine engine load and burn time. Notably, this includes the spark and knock calculations.
- Fudging the IFR probably throws off the transient fuel calculations.
- Fudging stoich (changing it from 14.62 to 14.0, for instance) would require compensating the Open Loop AFR table, but once that's done, I think a lot of things might just fall in line. Closed loop operation would still run at true stoich because that's where the sensors switch.
In other words, error has to be introduced somewhere and it will have side effects. The trick is to figure out which error(s) has/have the most benign side-effects to deal with.
I'm basically chasing the idea that any error introduced anywhere is going to have unintended side effects:
- Fudging the airflow tables will affect anything that uses calculated airflow (instead of MAP) to determine engine load and burn time. Notably, this includes the spark and knock calculations.
- Fudging the IFR probably throws off the transient fuel calculations.
- Fudging stoich (changing it from 14.62 to 14.0, for instance) would require compensating the Open Loop AFR table, but once that's done, I think a lot of things might just fall in line. Closed loop operation would still run at true stoich because that's where the sensors switch.
In other words, error has to be introduced somewhere and it will have side effects. The trick is to figure out which error(s) has/have the most benign side-effects to deal with.
07-25-2005, 06:26 PM
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Here is the way I do it.
1. Unplug the the MAF
2. Change the VE until most STFT+LTFT are negative. -3 to -5. You have to move PE out of the way or u go open loop.
3. Plug in MAF cahnge MAF table until STFT+LTFT are negative. -3 to -5.
4. Get WB and tune PE for A/F of 12.5 at peek torque and 13 Peek horse power.
WHEN YOU GO TO PE FEUL TRIMS GO TO ZERO and you are done no big deal.
1. Unplug the the MAF
2. Change the VE until most STFT+LTFT are negative. -3 to -5. You have to move PE out of the way or u go open loop.
3. Plug in MAF cahnge MAF table until STFT+LTFT are negative. -3 to -5.
4. Get WB and tune PE for A/F of 12.5 at peek torque and 13 Peek horse power.
WHEN YOU GO TO PE FEUL TRIMS GO TO ZERO and you are done no big deal.
