As you stated COMMANDED, it commands but that is not what the AFR will be due to other conditions

In this case it is most likely timing scaled to go lower as RPMs increase which would cause AFR to be richer

If your running boost I suspect upper RPMs are set for low timing

As said right now the blower is disconnected and I only have a FIPK filter (similar to the blackwing filter for the corvette).
VE table is stock, Timing table is stock (28* at WOT), MAF table is stock.
Only the IFR table has been changed, but at WOT I saw a constant MAP so the PCM is always using the same IFR value.

That the measured AFR is lower than the "commanded" is not so strange (IFR is maybe still not right), I just don't understand why it makes a slope. Like if the MAF was seeing more air than what it was.

Unless there are other factors that influences fueling that I don't see in Edit.
There is a PE vs coolant temperature, but at 200F the correction is zero.
The measured timing was also 28* without KR.

I know: the AFR is not too much out and I could correct it in the PE vs RPM table and call it a day. I just was wondering why it's a curve and not a line...

Thanks - Stefano

Short report

It's a while now that I changed the IFR table and the tune is still OK.
LTFT change a little depending on wheater conditions (go a little positive when cold) but that's OK.
What I did was log for LTFT, fuel trim cell and MAP.
LTFT are averaged, MAP is rounded to the next MAP value in the IFT table.
I used only cells 0-19.
I then put LTFT ans MAP in a pivot table (Excel).
The result is a correction in % of the specific IFR value.

So far so good!
I used to tweak the MAF table but never with good results. At least not as good as only changing the IFT table.
A side effect of changing the MAF table is a wrong G/cyl value which affect timing also!!!
I used to reduce the MAF values to adjust fueling: less G/sec means less G/cyl and in general higher timing than necessary (PING!)

Here the actual IFR curve: an untypical shape, but LTFT are now +/- 2% with an average of almost zero

Stefano

Good, glad to see your getting purged out of what you see on forums saying to screw with MAF and VE tables when as you saw it just blurs the results in scanner data and gets you no where to having clear fuel trims.

You cannot blindly use cells 0 to 19 as a bulk value since some cells are used for decel and fuel learn is off thus your trim average is bloated since its adding into the trim average when PCM is commanding fuel off thus would be leaner on decel but being added to when fuel is commanded on

I was thinking only in cell 21 the PCM will turn off fuel learn (in fact I see an AFR of around 13 on the WB but the LTFT remain constant at about -2%). During fuel cut off it's another story.
I also see cell 0,1, 4 and 8 in decel (mostly 0 and 1) but the AFR is stoichiometric (so I assume the PCM is learning).

What cells would you consider? I tried 0-19 and 0-15 and the result is exactly the same.

For MAP over 85 - 90 kPa it's quite difficult because it goes in PE, so I just continued the line by feeling (values 90 - 100 kpa). Is there another way to determinate this last piece of the IFR curve?

Stefano

Its not black & white on decel since engine changes have moved vaccum around, DEFCO or cell boundaries were changed via a tune, etc

There are really two conditions, certain cells like 21 are large lift of gas pedal but other cells are smaller lift but in both cases if not set to a conditional math in Excel would be added as if they were part of true LTFT averages.

Only setting conditions in the math in Excel can you find true values but in the end, again of trims are within -/+ 5% of STFT then PCM is ignoring LTFTs so you can chase a ghost that is not there.
As to WOT there is no performance difference if AFR is 12.4 or 12.6 so as long as there is no ping and timing is close to around 28 degrees for a NA engine then tweaking tune any more does not buy you anything.

Lastly cars are not driven like being on some chassis dyno so it must be considered that simple movement of gas pedal can skew trim averages but mean nothing to overall performace.

OK, I managed to separate the decel values in Excel.
It's true: it doesn't follow the cell numbers.
Mostly cell are 21, 0, 1 and 4. But not only.
Result: the same IFR line as I posted before.
I'm happy with the result, I just don't understand the shape of the curve at low MAP. It just doesn't make sense (to me).
Do you have an explaination?

Stefano

Not sure what your asking since as here is an example of a testrun and as engine load increases so does airmass which increases grams/cly to injector ON time

I just wanted to say that this IFR curve is a little strange in the low MAP range.

As you said Excel would average everything (also during decel)so I changed the spreadsheet to consider only the scan data related to acceleration and not decel.
Considering acceleration only doesn't change the IFR curve, so I guess this is what my engine wants.
(This curve is the result of a 2 hours scan, using only cells 0-19, cell 15 only when not in PE).
I was just surprised to see lower G/sec at 30 kPa than at 20 kPa.

Stefano

Stock engine at idle around sealevel is around 30-35 KPA Map. Compare 10-30 KPA when fuel learn is ON and you also see less then 30 KPA, torque less then 30 lbs to negative where 30 plus KPA engine is pulling more engine load and timing to maintain idle

Your values almost look like your scanner is backwards and not KPA but in inh

Being 100 KPA MAP would be WOT ( low vaccum) and 20 KPA ( high vaccum )