Hi all,

I would like to clarify the meaning of Fuel Trim Cells numbers but I still miss a lot of information and do not understand some parts of it. As far as I know there are 23 cells or less. But what do they mean? They store LTFT values (correction factors) for specific conditions. So starting from the last one, those conditions are:

Cell 22 - Power Enrichment mode (a kind of open loop mode in the closed loop mode <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> )
Does it mean WOT? I think it depends on how we define WOT (it does not have to be 100% TPS) but basically it should be the same.
Conditions for the engine to enter PE are defined in WOT Cold and WOT Hot tables (one is chosen based on actual engine ECT and Hot Temp setting). And the actual fuel values for PE are defined in PEvsTemp (adder) and PEvsRPM (multiplyer).

Cell 21 - Deceleration
Is it still closed loop (fuel corrected based on O2 readings) as I can see LTFT values changing for this cell as well?

Cell 20 - Idle
What are the conditions for the engine to be at that cell at idle because as I realized it is not the only cell for idle (see cells 18-19). For sure the engine is in this cell when it is first started. So is it a cell for open loop idle only?

Cells 18-19 - Idle as well?
Is it a closed loop idle or what? I realized that durring idle the engine can be in one of those three cells (18-20). What is the rule for this?
I also realized that with A/C on it stays in cell 18 and with the A/C off in cell 19. Can someone explain this, please?

Cells 16-17 - ???
I have never ever seen them on the Ease trace. Do they exist? What they are used for?

Cells 0-15 - normal driving
What cell is in use is based perhaps on RPM and Load (MAP) but I can be wrong here. What I could find is the following table for LT1

0 900 1200 2000 redline
0 +----+----+----+----+
| 0 | 1 | 2 | 3 |
30+----+----+----+----+
| 4 | 5 | 6 | 7 |
50+----+----+----+----+
| 8 | 9 | 10 | 11 |
80+----+----+----+----+
| 12 | 13 | 14 | 15 |
100+----+----+----+----+

Is it the same for LS1? Can you change table ranges somehow (I think it was possible for LT1 with LT1 Edit)?
Are those cells used only in closed loop? If yes what cells are used while driving in open loop (like when you start the cold engine and start driving before it switches to closed loop)?

Please share your knowledge on this topic with all of us.
Thanks,
MarcinK

 

i've seen trim cell
7 @ 65-82 mph
3 @ 78 mph
10 @ 19-24 mph

so it's not the same

 

I just averaged all MY Cells during a autotap run and this is what I came up with:

Normal Driving 1
-2.87 -2.39
Normal Driving 2
-3.19 -2.62
Normal Driving 3
-1.57 -1.48
Normal Driving 4
Normal Driving 5
-3.90 -1.60
Normal Driving 6
-1.21 -1.04
Normal Driving 7
0.92 0.95
Normal Driving 8
Normal Driving 9
-0.80 -0.40
Normal Driving 10
0.34 -0.23
Normal Driving 11
-0.34 -0.46
Normal Driving 12
Normal Driving 13
Normal Driving 14
-0.44 0.00
Normal Driving 15
-0.80 0.00
16
17
IDLE : AC=ON 18
IDLE : AC=OFF 19
-10.61 -10.61
IDLE 20
-7.92 -8.62
DECELERATION 21
-3.37 -2.98
WOT 22
-0.38 -0.20

<small>[ April 17, 2002, 11:46 PM: Message edited by: C5 YA ]</small>

 

If we knew how this rpm vs load table looks like for the LS1 we would be able to better tune for LTFT close to 0 at specific points. And if it would be possible to edit the boundaries we could make the table more usable. As when I installed my H/C setup I do not see cell 0 and 1 anymore on the traces (and those cells were used before).

MarcinK

 

This is a good thread. the 1-19 concept is good for generalization but I, too, have noticed that it is not as cut and dried as that.

The more info on this the better we can use to tune and diagnose problems.

Mark

 

I posted this to the LS1-Edit mailing list already but for those who might not be on that, I've made some plots to follow up on Marcin's question of the meaning of the FTCs. Using some data I collected for other purposes I determined the min, max, and average RPM and MAP for each FTC (0-19) for a number of collections. The plots below use the average values since it's a little easier to see cell centers.

average engine speed for each FTC

average MAP for each FTC

average cell centers

Although I haven't done any statistical manipulation of the data to allow for sample sizes, confidence intervals and the like, it does appear to be in good agreement with the structure of the LT1 tables Marcin posted. I think some more purposefully collected data would allow a sufficiently sharp determination of cell boundary estimates.

Note that I didn't have any data for FTCs 16-19 in these data sets (although no attempt to exclude it.) All the data came from my 98 A4 car.

A related question, has anyone collected calculated load values using AutoTap? All my previously collected data looks like 0. <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />

<small>[ April 18, 2002, 01:47 PM: Message edited by: ToplessTexan ]</small>

 

IMHO, to much is put on what each cell means from a tuning standpoint since for tuning purposes the 3 main areas to tune related to AFR and timing is :
Idle, Part throttle and WOT is simple cell 22.

Part throttle is the real work using cells 1-17 but if looking at the raw PCM data, the more engine load, the higher the MAF Freq is and that signal value determines which PT cell is used.

To make a simple graph, a city drive recorded :

<img src="http://teamzr1.com/pcmecm/cellvmaffreq.gif" alt="" />

Thus as MAF Freq increased, so did the cell being used.
Thus I convert to grms/sec and control tune across RPM range that way.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"> A related question, has anyone collected calculated load values using AutoTap? All my previously collected data looks like 0. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I tried once and had the same results as you.

I can send you my recent data with FTC and MAP to add to yours, but I'm not certain that it makes sense to mix the data. I've observed that FTC is very sensative to changes in the MAF. If you monitor FTC for a given TPS (holding speed, gear & terrain constant) and then change the MAF by 5 - 10% (e.g. to adjust your LTRIMs) you will observe a noticable change in FTC used.

 

Question about WOT and FTC:
A couple times in my autotap log, TPS is 100% but the FTC is 15 and the O2B1S1 and OSB2S1 are like is 0.10 and 0.18, respectively.
Is that normal?

 

</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>I can send you my recent data with FTC and MAP to add to yours, but I'm not certain that it makes sense to mix the data.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I can just dump it into a different database. I'll take either your ATL or CSV files. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"><strong>I've observed that FTC is very sensative to changes in the MAF. If you monitor FTC for a given TPS (holding speed, gear & terrain constant) and then change the MAF by 5 - 10% (e.g. to adjust your LTRIMs) you will observe a noticable change in FTC used.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I'm not wild about changing the MAF cal in general. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Sonny:
<strong>Question about WOT and FTC:
A couple times in my autotap log, TPS is 100% but the FTC is 15 and the O2B1S1 and OSB2S1 are like is 0.10 and 0.18, respectively.
Is that normal?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I've seen similar. Keep in mind that these values are time shifted relative to one another and are not really a "snapshot" at any given point in time.

 

</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>To make a simple graph, a city drive recorded :

<img src="http://teamzr1.com/pcmecm/cellvmaffreq.gif" alt="" />
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">John, that plot is just one step away from a pie chart. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

 

Topless: sent you 2 excel files

 

<img src="http://holdenls1.com/Temp/Maffreq.jpg" alt="" />

This is how EFIliveV5 can capture in real time for you.
Take no notice of the result inside the boxes, it just the spark timing, anyway see how you can change the horizontal and the vertical to what you want to log.
We can produce a CSV file as well.

<small>[ April 18, 2002, 10:15 PM: Message edited by: SIKLS1 ]</small>

 

Got 'em Ragtop, thanks.

 

OK here it is in a real simple form.

<img src="http://teamzr1.com/pcmecm/cellavg.gif" alt="" />

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by ToplessTexan:
John, that plot is just one step away from a pie chart. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> [/QB]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">

 

Here is what I found regarding idle cells:
20 - open loop idle - always used after start until the engine swithes to closed loop
19 - closed loop idle with A/C off
18 - closed loop idle with A/C on

Anyone disagrees?
MarcinK

 

With our foot on the floor accelerating through 1st, 2nd and 3rd gears, what would make the car switch back and forth from cell 22 to 15???

Thanks,

Eric