Which Cells for LTFT Averages?
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From: Albuquerque, New Mexico
Which Cells for LTFT Averages? I think I need to re-phrase this question. To get the non-WOT LTFT averages, do I use fuel trim cells 17 and down (non-idle) or cells 20 and down which include the idle?
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Re: Which Cells for LTFT Averages? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Ragtop 99:
<strong>try cells 1 - 19</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Inaccuratw when using cells 17,18,19,20 are all idle conditions and cell 21 is when lifting from gas pedal.
You want calls when under P.T load, not idle mucking up rhe LTFT load averages.
<strong>try cells 1 - 19</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Inaccuratw when using cells 17,18,19,20 are all idle conditions and cell 21 is when lifting from gas pedal.
You want calls when under P.T load, not idle mucking up rhe LTFT load averages.
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From: Whitby Ont Canada
Re: Which Cells for LTFT Averages? Okay so this article that I have been following is wrong LTFT/O2 analysis Would you be so kind to tell us which fuel cell trims that we should monitor so I can get this right?
<small>[ April 23, 2002, 10:01 PM: Message edited by: J&JsTA ]</small>
<small>[ April 23, 2002, 10:01 PM: Message edited by: J&JsTA ]</small>
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Re: Which Cells for LTFT Averages? Cells 0-15 are clearly part throttle cells. (Yes, there is a cell 0 and it's all but impossible to sample.) There has been some discussion about the remaining cells. I believe there is some variance among model years. In my 98 C5 I have never seen data from cells 16-19, 20 is idle, 21 decel and 22 WOT. Cells 18 and 19 have also been reported as CL idle and 20 as OL idle on some newer (99+) cars. These are easy enough to verify on your own car. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
Re: Which Cells for LTFT Averages? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Team ZR-1:
<strong>
...cells 17,18,19,20 are all idle conditions... You want calls when under P.T load, not idle mucking up rhe LTFT load averages.
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I looked at my ATAP and cells 17 & 19 are idle related (0% TPS) although cell 19 occurred sometimes while the car was moving slowly. Cell 18 did not appear.
Explain why I wouldn't take into account those cells since they come into play driving the car around town. For the sake of discussion, lets say the skew the data so that the change made to my base setting is effected by 1% (absolute terms, say average = +5% instead of +4%). How will this effect performance (e.g. gas mileage, throttle response, line presure used)
<strong>
...cells 17,18,19,20 are all idle conditions... You want calls when under P.T load, not idle mucking up rhe LTFT load averages.
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I looked at my ATAP and cells 17 & 19 are idle related (0% TPS) although cell 19 occurred sometimes while the car was moving slowly. Cell 18 did not appear.
Explain why I wouldn't take into account those cells since they come into play driving the car around town. For the sake of discussion, lets say the skew the data so that the change made to my base setting is effected by 1% (absolute terms, say average = +5% instead of +4%). How will this effect performance (e.g. gas mileage, throttle response, line presure used)
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From: Whitby Ont Canada
Re: Which Cells for LTFT Averages? When I went out last night to ATAP my 2002 WS6 TA/A4 for argument sake I did monitor cells 1-19 and did notice on a couple of occasions while waiting at a red light that the PCM was sitting in cell 19 with a LTFT of -3% thus having what kind of effect on my overall driving cell averages(giving false rich condition in the average)??? Ragtop you are right it was under running conditions but does it skew the averages to much of the other cells while the engine is under more stress and should we be including these cells in our average. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
<small>[ April 25, 2002, 01:14 PM: Message edited by: J&JsTA ]</small>
<small>[ April 25, 2002, 01:14 PM: Message edited by: J&JsTA ]</small>
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Verdad Gallardo TECH Apprentice
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From: Whitby Ont Canada
Re: Which Cells for LTFT Averages? Sorry...one more question to throw into the mix. What do the different categories/ranges represent... 1,2,3,4...19. They each must represent something different or they would use 1 category for PT(cruise) 1 for idle and 1 for WOT. Anyone?
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Re: Which Cells for LTFT Averages? Cells 17 and 18 are idle cells when A/C is on
Cells 19 and 20 are idle with A/C off.
Depending if engine is cold or hot will dictate which of the 2 cells is used.
Which cell is used is dicated on MAF flow in signal freq.
As the freq signal (load) increases so does which cell is used.
<img src="http://teamzr1.com/pcmecm/cellavg.gif" alt="" />
As you can see cells 0-6 are less then 10% engine load.
If your dialing in LTFT for best performance, I would not include any idle, or non load cells, for they effect the math answer because it includes them in the total number your dividing by to het a valid load average.
That excel file everyone seems to use is flawed, it includes all 19 cells as part throttle, claims WOT is only when TPS is 99.6 or greater and feels knock of 3 degrees or less of timing retard is a "don't care" when 3 degrees loss at WOT is a fair loss of performance, plus can mean PCM drops down to low octane timing table and in worst case might not go back to high octane table until PCM reads at least a 20% iincrease in gas gauge to reset low octane flag.
A check for refueling events is done at engine start. A refuel flag is set in KAM
if the fuel level at start-up is at least 20% greater than fuel fill at engine-off.
It stays set until the evap monitor completes Phase 0 of the test
<small>[ April 25, 2002, 06:52 PM: Message edited by: Team ZR-1 ]</small>
Cells 19 and 20 are idle with A/C off.
Depending if engine is cold or hot will dictate which of the 2 cells is used.
Which cell is used is dicated on MAF flow in signal freq.
As the freq signal (load) increases so does which cell is used.
<img src="http://teamzr1.com/pcmecm/cellavg.gif" alt="" />
As you can see cells 0-6 are less then 10% engine load.
If your dialing in LTFT for best performance, I would not include any idle, or non load cells, for they effect the math answer because it includes them in the total number your dividing by to het a valid load average.
That excel file everyone seems to use is flawed, it includes all 19 cells as part throttle, claims WOT is only when TPS is 99.6 or greater and feels knock of 3 degrees or less of timing retard is a "don't care" when 3 degrees loss at WOT is a fair loss of performance, plus can mean PCM drops down to low octane timing table and in worst case might not go back to high octane table until PCM reads at least a 20% iincrease in gas gauge to reset low octane flag.
A check for refueling events is done at engine start. A refuel flag is set in KAM
if the fuel level at start-up is at least 20% greater than fuel fill at engine-off.
It stays set until the evap monitor completes Phase 0 of the test
<small>[ April 25, 2002, 06:52 PM: Message edited by: Team ZR-1 ]</small>
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From: Murphy, TX
Re: Which Cells for LTFT Averages? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Team ZR-1:
<strong>Which cell is used is dicated on MAF flow in signal freq.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">John, can you cite a reference for this statement?
My understanding (from the factory service manual) is that "the long term fuel trim is a matrix of cells arranged by MAP and RPM." While I understand that MAF frequency is correlated, I do not agree that LTFT is a function of MAF frequency. If it was, the MAFT would not do what it does. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
<strong>Which cell is used is dicated on MAF flow in signal freq.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">John, can you cite a reference for this statement?
My understanding (from the factory service manual) is that "the long term fuel trim is a matrix of cells arranged by MAP and RPM." While I understand that MAF frequency is correlated, I do not agree that LTFT is a function of MAF frequency. If it was, the MAFT would not do what it does. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />