Why is the MAF so innaccurate?

[redhardsupra]

maffreq and mafflow are enough, but all the other usual suspects are always useful.

[diynoob]

Log file attached to this message. Some BENs in the MAF curve are a bit high or low -- but everything around them makes sense and is close. So I didn't tweak just one cell in the MAF table down before it was showing rich or lean. My assumption is if the MAF curve would get out of whack to dial in air/fuel then that means that there is something else wrong in my tune. I couldn't feel it so I just left it alone.

Any help you can offer is appreciated. I have to work to keep my car above 1K RPM because now that I have the MAF back on, the car wants to stall a lot more.

[Bruce Melton]

I had a similiar phase were I could not MAF dialing to make sense. I found that I had to go back and make sure all was closed up from the AutoVE mode then change ONLY this:

Step by step:

0. Assuming a calibrated VE using speed density mode and "AutoVE"...
1. Put the tune in closed loop and all normal PE, etc.
2. Disable LTFT {B3801} and STFT idle trims {B4108}.
3. Log a bunch of data - normal driving, wide open (to hit the high Hz, do some bonzai 4th gear 100+ mph runs
4. Save the log file.
5. Filter the throttle transients out using the BEN filter.
6. Copy and paste the MAF map as a factor into your MAF table in the tune.
7. Repeat steps 3 through 6 and you'll have the MAF dialed.

My MAF is dialed in to within 1% from 2375 Hz to 11k+.

Then it all came together as it should. Make sure you have the right MAF table for your car.

[dc_justin]

I had a similiar phase were I could not MAF dialing to make sense. I found that I had to go back and make sure all was closed up from the AutoVE mode then change ONLY this:

Step by step:

0. Assuming a calibrated VE using speed density mode and "AutoVE"...
1. Put the tune in closed loop and all normal PE, etc.
2. Disable LTFT {B3801} and STFT idle trims {B4108}.
3. Log a bunch of data - normal driving, wide open (to hit the high Hz, do some bonzai 4th gear 100+ mph runs
4. Save the log file.
5. Filter the throttle transients out using the BEN filter.
6. Copy and paste the MAF map as a factor into your MAF table in the tune.
7. Repeat steps 3 through 6 and you'll have the MAF dialed.

My MAF is dialed in to within 1% from 2375 Hz to 11k+.

Then it all came together as it should. Make sure you have the right MAF table for your car.

If you want to tune the MAF rapidly without having to worry about any input from the VE table, set parameter B0120 = 0 or 200 or some very low RPM. Any rpm point above that parameter value will result in using the MAF exclusively for airflow.
Edit: Re-read your post. Closed loop with BEN's does not work, as the O2 sensors will adjust fueling to stoich. You need to remain in open loop and re-enable the MAF, then disable airflow calculations.

[redhardsupra]

raw data, no filtering:



Z-score based filtering, 2 sigma:



Z-score based filtering, 1 sigma:



few things become apparent once you chart your dataset:
1. you need more data, especially in mid/upper range
2. even the simplest statistical filtering works, however, for it to work well, it needs lots of data--look at the topend where data is so scarce it doesn't know what to do with it.
3. you're using BEN's to adjust your MAF table right? that's one way to do this. i prefer to use dynair values mapped onto maffreq scale for this particular calibration. this way ve table and maf table are truly describing the same thing, just in two forms. if you do two tunes, one to adjust ve, and another to adjust maf, that's two separate tunes. they'll be close, but since they operate from two different datasets, they are describing two different tunes really. try my method sometime, maybe it will work better for you.

i'll try to port this method to calc pids, right now it's in excel, cause it's simple to prototype things this way. i can post the spreadsheet if you're interested, as this was actually much harder to do in excel than i originally thought, so there's some really useful tricks in there.

hope this helps,
Marcin

[joecar]

Marcin,

That's a good bit of research you have done...

The raw data shows more scattering in the upper range...would I be right in saying that the MAF is not as consistent in the upper range, or is this due to something else...?

Yes, please post the spreadsheet, that would be great.

Cheers,
Joe

[ringram]

5.7 Hemi's run speed density only.
If its good enough for them .....

[Garry]

5.7 Hemi's run speed density only.
If its good enough for them .....

[joecar]

Yep, never have to worry about a failed MAF...

[Tordne]

You'd think it must answer the question (as does the HSV GTS) about the effects of weather and altitude change. Australia, like the US can experience a wide range of extremes...