Okay, after thinking about my theory of my car getting the starvation diet for fuel, I decided to go and return the pe vs rpm to the stock table and then after doing that I added 103 percent to the PE vs. RPM table.
I took the car out for an hour and did two logging sessions with multiple restarts.
The above chart shows the end result, disregard the text avg for fuel trim cells 1-19 it is actually only using 1-17 I just haven't changed the text.
My LTFT's went up slightly which I don't understand since I did not modify the MAF table. Cell 22 still has 0 in all the ltft's data.
The timing is more consistant and actually does goes over 22.5 degrees than in my previous logs.
The car feels much stronger in the upper midrange and top end when pulling from say 4 grand.
Can someone possibly explain any of this to me? It almost seems opposite of certain behaviors I expected.
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My guess and that's all it is, just a "guess", your average LTFTs went up (reflecting a richer correction factor, but not sure) b/c of IAT being so much lower (denser) during your most recent relearning period. IAT=54.5F implies relatively cold OAT which should increase frequency of the MAF sensor's output during closed loop variable load driving conditions. (Man, it's darn right cold there in Lost Wages this time of year).
What's a bit strange is that your ECT is still about the same as before during your dyno test today. 195F seems a bit high for
such a relatively low OAT. Do you have a stock tstat? Is that the lowest you've seen the ECT of your DIC? (Mine is still stock, and under comparable OAT driving conditions, it generally stabilizes at 190F. If your's is stock also, the difference can probably be explained by factory variation allowable tolerances for the tstat.
BTW, the "stronger" SOTP you're feeling could also be attributed to the colder OAT driving conditions.
Interesting observation, I guess the IAT could have an effect on the LTFT's since it did only vary by approx 1/2 of 1 percent.
I am running a stock thermostat and 195 seems to be about average temp for me, I will probably switch it out very shortly since I have modified my fans a little anyway.
The air was very brisk and that could definately been part of the power increase, but now that I think about it, I wonder why running pe vs rpm at 103 percent of the normal table did not change my WOT osb1 and osb2 by much at all?
Originally posted by Z06_2002 I wonder why running pe vs rpm at 103 percent of the normal table did not change my WOT osb1 and osb2 by much at all?
Stock O2 sensors are not accurate at WOT. Do not try to tune with them. In addition, the Excel sheet you are using has some design flaws. For example, it does not even consider data transition points (when you lift in the middle of a scan line).
You have to use a wideband for WOT A/F readings.
How were you logging this data? Are you pulling some WOT data out of a cruising log? IMO, if you want to log WOT data you should either do a 1st - 4th gear blast, or a 4th gear low-rpm dyno like roll-on. The log should only be running during your blast. Do not pick WOT data points out of a big log created while driving around.
Until I find a wide band o2 dyno, I am still gonna have to play test n tune. I agree the osb1 and osb2 are not very accurate but I am gonna make small changes back and forth and re-dyno. Worst case scenario is I can always go back to the original settings I have verified with my last dyno. I cannot wait to use the new EASE program I ordered it averages everything automatically, Tuesday if all goes well it should be here.
Originally posted by Z06_2002 Until I find a wide band o2 dyno, I am still gonna have to play test n tune.
Trying to tune PEvsRpm without a wideband is a waste of your time. The stock O2 sensors are not only inaccurate at WOT, they are pretty much worthless.
Trying to tune PEvsRpm without a wideband is a waste of your time. The stock O2 sensors are not only inaccurate at WOT, they are pretty much worthless.
Good luck.
Yup, you are absolutely right, I just returned to the dyno tune settings, and until I get a wideband dyno I will just leave it alone.
I'm confused. The first set of ATAP data (presumably taken during dyno session on Saturday), compared side by side with subsequent data taken with 103% multipliers in WOT PEvs.RPM table, are as follows:
NOTE: All WOT O2 sensor readings are in question for a variety of reasons. First, purely mathematical; the averaged values on the last line are calculated too low for both sets of readings. Second, something is odd about O2SB2s1 readings in comparison to O2SB1s1. The value decreased for B2, but increased for B1. That really does not make any sense to me. I would have expected both banks to either decrease or increase together from the initial bank reading respectively. B1 seems to be responding to the PEvs.RPM table change, but B2 is not. Either these readings are totally bogus or something else is happening.
General Observations:
1) The change from -0.4611 to +1.04884 in averaged LTFTs is far greater than a couple of percent. It's more like 200% relative to initial values!!! Note that left and right banks both started out as "negative" values and afterwards changed to positives.
2) LTFT for B1 and B2 (left and right banks) both changed significantly and relatively consistently. The deltas are +1.533 and +1.497 respectively. This trends suggests both pre-cat O2 sensors are "Tracking" fair closely together and so must each bank of associated fuel injectors over a variety of engine load conditions.
3) The absolute value of the OEM O2S signal outputs may be of questionable accuracy, but they tend to "change" voltage signal amplitudes fairly consistently (with respect to each other) over a range of operating load conditions. So, value changes from one test case to another can be taken more seriously for trend analysis purposes.
4) If the intent of changing PEvs.RPM table multipliers +3% from factory defaults, in order to further fuel enrich WOT operation, just the opposite seems to have occurred.
5) Conversely, something happened to cause LTFTs to be biased richer over a range of part throttle and engine load conditions.
Conclusions:
1) The only thing evident within these two sets of data log data point is the fairly significant drop in the intake air temp (IAT) which means the AFR, all other things being equal and kept "as is" by the PCM, should have become leaner.
2) This analysis of before and after changes to the PE vs. RPM WOT table, points out the interactiveness of having fuel cells 1-17 LTFT offsets drift off much further from zero, and the difficulty that has on trying to tune AFR at WOT.
RB, I'd be interested in your comments. You seem to have a much better handle on all this kind of stuff than I ever will.
I am not sure why you are comparing data logged while on a dyno to data logged while on the street. The operating conditions are much different.
I have no idea how you are averaging LTFT. You are being much too vague with this. Are you taking average LTFT readings from a dyno run? That would be the wrong thing to do. Dyno runs are at WOT. They are not closed loop street cruises.
When I look at closed loop LTFT trends on the street I group all data by the 22 individual cells and take a look at each cell. I eliminate the data transisition points (when you change cells in the middle of a scan line). I take a look at the average values for each cell. I do not look at one big average because that is very misleading.
A LTFT change from -.5 to +1 is no big deal at all. The car is designed to run like. You are worring way too much about changes in LTFT. The car is designed to change things around as operating conditions and weather conditions change.
Don't bother trying to compare average values from the stock O2 sensors at WOT. In addition, that Excel sheet is plagued with errors. It is not "averaging" the values correctly, and even if it was you would be chasing your tail.
Put your car in 4th and do a 2000 - 5500 RPM WOT roll on while recording O2 B1S2 and O2 B2S1. Make no changes and log another run. The O2 sensor values will differ from run to run.
I'm still confused . . . wouldn't LTFT values stored in each cell be just as inaccurate at O2S readings in real time. They are both based on the same thing, the O2 sensors. The accumulation of STFT values, averaged over time to become LTFT values, all share the same source of measurement . . . the O2 sensors.
Yet, everyone who seems to know something about tuning, say to use a scan tool to datalog, then fine tune (MAF table or whatever), datalog again, check for changes to LTFT, fine tune some more, datalog, etc, etc, until LTFT are essentially nulled out as much as possible. Most people try to get their LTFTs, via an accumulative average of all non-WOT fuel cells, within +/- 0.5 of zero. Some tuners are okay with LTFTs as much as +/- 4 of zero.
The point is to fine tune (via MAFT or LS1Edit table or whatever adjustments), under a wide variety of part throttle, non-WOT load conditions, until their average LTFTs are close to zero (or just slightly negative).
What's the point if the O2 sensors produce inaccurate readings or are not to be trusted?
Or, is it true that the O2 sensors are actually very accurate (450mV) at exactly 14.7:1 AFR operating conditions?
O2 sensors are very fast & accurate during closed loop operation. They work very well around 14.7:1. When running closed loop at 14.7:1 the O2 sensors will bounce back & forth like a sine wave between about 100 to 900mv. The PCM reads O2 sensor feedback & maintains LTFT while running closed loop. LTFT values can and will vary a bit as the conditions & weather changes. You can't drive yourself crazy looking for specific LTFT values because they are designed to change.
The PCM goes "open loop" and does not read the O2 sensors when you are really at WOT, PE, TPS >98, MAP >~25. This can be seen in ATap, Ease, EFILive, etc. If the stock O2 sensors really were accurate and reliable at WOT I would think that GM would use their feedback at WOT.
How about "weighting" the fuel trim cells LTFTs, i.e. the higher the cell# the greater its weight. Would that correspond to meeting the objective of trying to null out the LTFT "baseline" at WOT?
Are cells 1-17, used in sequential order roughly in proportion to the load on the engine (and increasing amount of TPS)? Is one fuel map Cell more important to monitor and use for "the avg", than others?
Does anybody know how exactly the PE WOT (open loop) fuel cell (22?) map derives it's LTFT offset? Is it a very slow accumulation process before it eventually reaches a relatively stable value or is constantly changing? If so, what is its dynamic range?
Originally posted by dsinned How about "weighting" the fuel trim cells LTFTs, i.e. the higher the cell# the greater its weight. Would that correspond to meeting the objective of trying to null out the LTFT "baseline" at WOT?
Are cells 1-17, used in sequential order roughly in proportion to the load on the engine (and increasing amount of TPS)? Is one fuel map Cell more important to monitor and use for "the avg", than others?
Does anybody know how exactly the PE WOT (open loop) fuel cell (22?) map derives it's LTFT offset? Is it a very slow accumulation process before it eventually reaches a relatively stable value or is constantly changing? If so, what is its dynamic range?
No need to weight. The point of zeroing, or getting a slightly negative LTFT, is that once you enter Power Enrichment mode and start to get the extra fuel defined in those tables, your LTFT will lock at zero, and not add another variable for you to consider for fuel needs. A positive LTFT (lean) will carry into PE mode, and it can vary, so whatever amount you add in PE vs RPM will never be right.
The cells are grouped and selected based on RPM & Calculated Load. They are not sequential. Also, several can result in PE mode, it's not always cell 15 or 22. That's why your analysis needs to be more detailed.
John Rovner, Team ZR-1, put the following cell map together:
Fuel Trim Group 1, Cells 0 - 3
FTC 0 - 2 slight deceleration, little to no load
FTC 3 low load, power enrichment
Fuel Trim Group 2, Cells 4 - 7
FTC 4 low load, part throttle
FTC 5 low load, part throttle
FTC 6 moderate load, part throttle
FTC 7 moderate load, part throttle, power enrichment
Fuel Trim Group 3, Cells 8 - 11
FTC 8 - 10 moderate load, part throttle
FTC 11 moderate load, part throttle, power enrichment
Fuel Trim Group 4, Cells 12 - 15
FTC 12 - 14 higher load, power enrichment
FTC 15 higher load, power enrichment, wide open throttle (EPA definition @ 100% Load)
Fuel Trim Group 5, Cells 16 - 19
FTC 16, Automatic transmission in "Park" or "Neutral", hot idle, a/c on
FTC 17, Automatic transmission in "Park" or "Neutral", hot idle, a/c off
FTC 18 hot idle, a/c on (Manual or Automatic transmission in "Drive")
FTC 19 hot idle, a/c off (Manual or Automatic transmission in "Drive")
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