MAF Calibration..Why not use SAE MAF vs CYLAIR DMA

[WeathermanShawn]

Question pertains to the advantages and disadvantages of calibrating the MAF using CYLAIR DMA vs just using SAE MAF.

If I know my MAF Frequency (hz) and I know my Air flow rate from my MAF sensor (SAE. MAF grams) why do most suggest instead calibrating it to CYLAIR DMA or as some have suggested to DYNCYLAIR DMA (dynamic)?

While I generally understand that this is to compare your MAF flow to your actual 'calculated' flow..Why is it improper to actually compare what your MAF is flowing vs the frequency? If the contribution of the MAF flow and its interaction with the VE table derived airflow is ultimately the sum of the two...Why measure the MAF flow against that sum?

To clarify, can I just use MAF frequency and SAE MAF, as my flow calibration?

[SSpdDmon]

IIRC, CYLAIR_DMA is used when the MAF is actively influencing your fueling. In other words, it should report the value used by the PCM that represents both blended (MAP + MAF) and non-blended (MAF only), calculated air mass values.

When the MAF is disabled, DYNCYLAIR_DMA is what you need to use as this is the lookup for the calculated air mass value used by the PCM in SD.

FYI for those reading - DMA = Direct Memory Access. :)

[WeathermanShawn]

SSpdDmon.

I was getting hung up on mistakenly 'calibrating' my MAF 'flow' using MAF Hz vs SAE.MAF.

How do you do it? AFR's, or do you concur with the theory of calibrating MAF Hz Vs DYNCYLAIR_DMA?

I know you have done some variations of IFR/MAF tuning. I ran into some problems with WOT AFR's when I experimented with IFR tuning. Of course I just used an arbitrary IFR % change for all MAN VAC's.

[SSpdDmon]

Copy that SSpdDmon.

I was getting hung up on mistakenly 'calibrating' my MAF 'flow' using MAF Hz vs SAE.MAF.

That didn't work.

How do you do it?

AFR's, or do you concur with the theory of calibrating MAF Hz Vs DYNCYLAIR_DMA?

I know you have done some variations of IFR/MAF tuning. I ran into some problems with WOT AFR's when I experimented with IFR tuning. Of course I just used an arbitrary IFR % change for all MAN VAC's.

Thanks.

..WeathermanShawn..
Me personally - I'm running a Procharger with full exhaust on a stock MAF curve. Most here won't agree with that (not the point of discussion now though). IMO - it's just another one of the various ways to skin the proverbial cat.

If I was going to "recal" my MAF, I'd first set the injectors to where I wanted them (regardless of tuning method) and depending on the mods - blend in a fudge factor to avoid a dangerously lean condition. Then, I'd set the MAF threshold to something unusually low (i.e. 200rpm) to put the car in a pure MAF mode. This would set me up for tuning via commanded vs. actual AFR. Do a few rinse & repeats by carefully logging and filtering and it should be pretty damn close.

What you have to be careful with is...we're talking two different things here. Air mass vs. air flow. The MAF is flow because it's in grams per second where as the PIDs above are grams per cylinder. The ones above are critical for tables like the High/low/base timing maps. If you don't know the correct air mass, you can't locate the correct cell in the map. In order to get a "base" MAF curve via the VE tables calcs in SD mode, I think you need the DYNAIR PID. :)

[joecar]

SSpdDmon is saying to do the same procedure as AutoVE but with the MAF enabled, and using a "MAF" BEN table
(i.e. having the same dimensions and units as B5001)... and (after filtering) multiplying the BEN's into B5001.

To do AutoMAF, you also have to set B0120 to some low value.

BEN is the ratio of the actual (wideband) and commanded AFR's.

[mr.prick]

or you can log GM.MAF and,
paste straight across. (w/o WBO2)

[joecar]

You mean DYNAIR or whichever one it is.

[mr.prick]

the last time i played with the MAF (loooong ago)
i compared BEN and GM.MAF,
multiplying BEN ended up giving the same values as pasting GM.MAF (lbs/min)
straight to {B5001}.

GM.DYNAIR or even SAE.MAF may give the same results,
i tried GM.MAF as an experiment but, i use BEN with RTACS.

[joecar]

GM.MAF is the value the PCM reads from B5001...

Multiplying GM.MAF by BEN should work good... (you still need to log MAFFREQ to know which cell in B5001).

[mr.prick]

GM.MAF is the value the PCM reads from B5001...

Multiplying GM.MAF by BEN should work good... (you still need to log MAFFREQ to know which cell in B5001).

yes,
column = RPM or what ever
row = MAFFREQ
data = GM.MAF

then just paste the logged GM.MAF data to {B5001}
it will be comparable to multiplying BEN.

[WeathermanShawn]

GM.MAF is the value the PCM reads from B5001...

Thats the one that had me confused. For some reason assumed it was calculated. Appears to be a table look-up based on user input.

Thanks for the information.