Why not use MAF for entire RPM range?

[DrX]

Yes, this is why it is very important to get the VE table correct (and avoid any portion of it being lower than actual)... i.e. if the VE table correctly allows the correct torque to be calculated, then the transmission will survive...

but it would be nice to have a non-failed SD mode.

The VE table will not be "correct" with respect to torque calculations if there has been injector scaling or if the base fuel pressure is different than stock. I have adjusted my trans pressure tables accordingly though. I have a trans pressure gauge and I can confirm that pressure does still vary with torque as commanded.

[joecar]

If fuel pressure is different than stock then the IFR needs to be recalculated to match;

if the IFR is correct (matches FP and injectors) then the corrected VE will correctly model the engine's air fill;

if the VE correctly models the engine's air fill then several things all work correctly (according to values populating these tables):
- spark timing advance,
- engine torque calculation,
- engine torque/traction limiting/protection,
- electronic throttle control,
- transmission line pressure calculation/control,
- transient fueling,
- and a few others.

Now, some large engines exceed the ability of the PCM to read MAF or to control injectors, so people will peform scaling to work around these limitations, but when this is done, those things I listed have to be addressed.

[redhardsupra]

What would be "really nice" is to have a section of the COS that "reverse populates" the MAF data from the VE table. In this way, the PCM/ECM is fed a value that it thinks is coming from the MAF and continues to run normally. It might be that the existing gm/Cyl value, which is calculated from the VE, is converted to gm/Sec on the fly using the MAF calibration table as a correction. Or maybe the existing "speed density air flow per second" values can be used directly and the MAF signal just ignored.

Simon.

I've done that, you can calculate the entire VE table from MAF, or vice versa. It's very simple, you can just do it with histograms. You set up a MAF calibration-like table, except for the airflow data you use not MAF data, but the results of the SD calculations.
getting VE out of MAF is a bit more complicated, but you start with setting up a VE-like table, and then for data you must use a custom pid, that takes MAF airflow (which is a lookup, and if it's calibrated correctly, then it's a correct lookup), and using the SD equations you can calculate VE (or GMVE) out of it. It's basic algebra, and it saves you a boatload of time. There is no need to calibrate the two tables separately. Although, doing it independently is a nice verification that both calibrations are correct, because if the resulting airflow from the two methods varies in a non-trivial manner, then you screwed up somewhere.

The one thing I'd like to work out in the future how to use both sets of data to figure out the cleanest data to use for the calibration. If we got two airflow estimators, why not use them both, and limit ourselves to just one of them? Any ideas?

[swingtan]

I've done that, you can calculate the entire VE table from MAF, or vice versa. It's very simple, you can just do it with histograms. You set up a MAF calibration-like table, except for the airflow data you use not MAF data, but the results of the SD calculations.
getting VE out of MAF is a bit more complicated, but you start with setting up a VE-like table, and then for data you must use a custom pid, that takes MAF airflow (which is a lookup, and if it's calibrated correctly, then it's a correct lookup), and using the SD equations you can calculate VE (or GMVE) out of it. It's basic algebra, and it saves you a boatload of time. There is no need to calibrate the two tables separately. Although, doing it independently is a nice verification that both calibrations are correct, because if the resulting airflow from the two methods varies in a non-trivial manner, then you screwed up somewhere.

The one thing I'd like to work out in the future how to use both sets of data to figure out the cleanest data to use for the calibration. If we got two airflow estimators, why not use them both, and limit ourselves to just one of them? Any ideas?

Yes, I've done that as well. Using the "VVE" in my case and setting up custom PIDs to get gm/S I was able to show the differences in airflow between the VVE and MAF, especially on transients. The problem is that that's only going to work in the Scan tool and has no impact on the ECM its self. It would be nice if the the OS could be set to feed the "MAFSD" data back into the OS to be used as the MAF data. Then things like Auto shifts would be easier to work out ( though still not perfect if you've had to bump the VE for changed injectors ).

On the auto shifts ( which I'm not an expert on ) I've been logging the estimated engine torque and then using that to "correct" the shift pressures. I can read the torque figures that the ECM is calculating and then I use that value for shift pressure adjustment. Fine tuning is then done in the force motor table. It seems to work OK, but may not be the ideal method.

Simon

[DrX]

The VE table will not be "correct" with respect to torque calculations if there has been injector scaling or if the base fuel pressure is different than stock. I have adjusted my trans pressure tables accordingly though. I have a trans pressure gauge and I can confirm that pressure does still vary with torque as commanded.

Oops! Should have said "if the base fuel pressure changes." Not that this is common, but I was thinking of my dual base pressure fuel system. As there is only 1 IFR table, there was compensation in my Boost VE table for the higher base fuel pressure when in boost.