Negative LTFT's of -8 to -10 creating Poor Off Idle response and Poor Part-Throttle..
07-08-2002, 08:54 PM
#1
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Negative LTFT's of -8 to -10 creating Poor Off Idle response and Poor Part-Throttle.. I believe I am having poor off Idle Throttle response while seeing -8 to -10 LTFT's. Also, worse than usual gas mileage and worse than optimum part-throttle response.
Technique #1 - To date I've done my ATAP runs usually a little bit of WOT then would drive a bit part throttle. I'd sort out the data into NON 21/22 cells and avg 1-19 for my LTFT's. Then I would sort the WOT 99.6% TPS and Cell 22 data.
This week for the first time in years I did not only that but also extensive part throttle and around town driving with NO-WOT runs. I'll call this technique #2 with 5 solid minutes of part throttle data and no WOT.
I found that technique #1 gave me avg LTFT's of 0 to -3. Technique #2 gave me -8 to -10. QUITE A DIFFERENCE.
I have been having issues with off idle and part throttle response. Given the above, I notched back from +15 Base to +10 and off idle seems QUITE improved.
So was my PCM on average just dumping too much fuel and having to pull it out with Negative LTFT's all the time and harming my off idle and part throttle, or is this all in my head SOTP? I will re-ATAP in another week.
I also would prefer +1 to +5 LTFT's with the PCM advancing timing and adding fuel over negative LTFT's.
Anyone want to comment? Reality checks?
Different logging of the data really changed things. Anyone experiencing super FAT A/F ratios early on a dyno WOT run might want to consider the same with a too rich base setting, right?
Technique #1 - To date I've done my ATAP runs usually a little bit of WOT then would drive a bit part throttle. I'd sort out the data into NON 21/22 cells and avg 1-19 for my LTFT's. Then I would sort the WOT 99.6% TPS and Cell 22 data.
This week for the first time in years I did not only that but also extensive part throttle and around town driving with NO-WOT runs. I'll call this technique #2 with 5 solid minutes of part throttle data and no WOT.
I found that technique #1 gave me avg LTFT's of 0 to -3. Technique #2 gave me -8 to -10. QUITE A DIFFERENCE.
I have been having issues with off idle and part throttle response. Given the above, I notched back from +15 Base to +10 and off idle seems QUITE improved.
So was my PCM on average just dumping too much fuel and having to pull it out with Negative LTFT's all the time and harming my off idle and part throttle, or is this all in my head SOTP? I will re-ATAP in another week.
I also would prefer +1 to +5 LTFT's with the PCM advancing timing and adding fuel over negative LTFT's.
Anyone want to comment? Reality checks?
Different logging of the data really changed things. Anyone experiencing super FAT A/F ratios early on a dyno WOT run might want to consider the same with a too rich base setting, right?
07-09-2002, 01:51 AM
#2
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Re: Negative LTFT's of -8 to -10 creating Poor Off Idle response and Poor Part-Throttle.. Keep in mind being the PCM has a slow processor and it is adaptive learning, every time the engine is shut down the RAM in PCM is erased and STFT registers live in that RAM and they are read by the PCM every 10 minutes of run time.
So by keeping that in mind, a cold start, STFT is blank and 1st 10 minutes will have averages for those conditions, now lets say you pick the pace up and engine gets hotter, now the STFT averages will effect the PCM decisions next time it cycles for a read.
Mix some higher engine load and average changes again, so what I am saying is plot your changes or driving style and consider STFT read times of PCM to react.
Remmeber in the old days to read a sparkplug we would put in brand new ones, do a drive and then shut off engine without lifting on gas pedal so it did not mask the AFR color of plugs to be read.
Or in another way, those scanner templates people use glump 6,000 PCM cycles of a recording and that means to get a average you divide by 6,000 thus you can hide ill performance values real easy as lets say LTFT did go real lean in a certain RPM but in 6,000 cycles you did very little at that RPM thus average is skewed and hiding important findings.
So by keeping that in mind, a cold start, STFT is blank and 1st 10 minutes will have averages for those conditions, now lets say you pick the pace up and engine gets hotter, now the STFT averages will effect the PCM decisions next time it cycles for a read.
Mix some higher engine load and average changes again, so what I am saying is plot your changes or driving style and consider STFT read times of PCM to react.
Remmeber in the old days to read a sparkplug we would put in brand new ones, do a drive and then shut off engine without lifting on gas pedal so it did not mask the AFR color of plugs to be read.
Or in another way, those scanner templates people use glump 6,000 PCM cycles of a recording and that means to get a average you divide by 6,000 thus you can hide ill performance values real easy as lets say LTFT did go real lean in a certain RPM but in 6,000 cycles you did very little at that RPM thus average is skewed and hiding important findings.
07-09-2002, 07:38 AM
#3
Re: Negative LTFT's of -8 to -10 creating Poor Off Idle response and Poor Part-Throttle.. Have you checked out this thread? https://ls1tech.com/ubb/cgi-bin/ulti...;f=23;t=000369
I am working on that right now. Trying to get my Ltrims a little below 0.
The thread discussion seems to show a good way of doing it. Albeit longer. You get an average of your ltrim at the maf frequency. It won't be lumped in with other maf frequency's, just the ones around. At least that is how I take it by scanning over it.
I tried scaling the data by 105% and it left me with idle being -.5 - 0.5 and my wot -4.
Eric
<small>[ July 09, 2002, 09:35 AM: Message edited by: wizkid ]</small>
I am working on that right now. Trying to get my Ltrims a little below 0.
The thread discussion seems to show a good way of doing it. Albeit longer. You get an average of your ltrim at the maf frequency. It won't be lumped in with other maf frequency's, just the ones around. At least that is how I take it by scanning over it.
I tried scaling the data by 105% and it left me with idle being -.5 - 0.5 and my wot -4.
Eric
<small>[ July 09, 2002, 09:35 AM: Message edited by: wizkid ]</small>
07-09-2002, 09:58 AM
#4
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Re: Negative LTFT's of -8 to -10 creating Poor Off Idle response and Poor Part-Throttle.. Ugh. I'm confused.
After further reading, I guess I'll target 0 to -5 LTFT's. People are saying that is more accurate for tuning WOT later.
Thx guys.
After further reading, I guess I'll target 0 to -5 LTFT's. People are saying that is more accurate for tuning WOT later.
Thx guys.
07-09-2002, 04:37 PM
#5
Re: Negative LTFT's of -8 to -10 creating Poor Off Idle response and Poor Part-Throttle.. My qeustion is this:
Does the LTFT condition at idle have any effect on WOT performance? If it doesn't, why not tune idle in for what it needs to be and then do part throttle stuff seperately?
ERic
Does the LTFT condition at idle have any effect on WOT performance? If it doesn't, why not tune idle in for what it needs to be and then do part throttle stuff seperately?
ERic
