Help with some air pid's

[Extinct]

OK, went out and did some scanning. Was going to work on calibrating my MAF.

I need some help understanding all these different pid's though. What the hell is the difference between them. I mean, SAEMAF vs GMMAF ? or GMDYNCYLAIR vs CYLAIR vs DYNCYLAIR_DMA vs CYLAIR_DMA vs DYNAIR ?

The right click - more info doesn't work on any of these ??

Same with all the different throttle positions.

I thought they would be identical, but you know what, when I log them, they don't report identical data - slightly different - see attached ???

[Blacky]

SAE.MAF - C.A.R.B. Mandated PID that returns airflow in grams per second. GM (and all manufacturers) are required by law to provide this PID. Also, C.A.R.B. mandated a scaling that is different from the GM.MAF version of this PID. Therefor you will see slightly different values due to different processing required to format each value.

GM.MAF - see above.

GM.DYNAIR - GM's estimated airflow in grams per second based on the VE table. This value is calculated independantly of the MAF. It is used to test MAF rationality and when the PCM is in speed density mode (i.e. MAF removed or disabled).

CALC.CYLAIR - EFILive's calculated grams/cylinder value. It is calculated as {SAE.MAF.gps}*15/{SAE.RPM}

GM.DYNCYLAIR - GM's estimated airflow in grams per cylinder based on the GM.DYNAIR value.

GM.CYLAIR_DMA - internal (DMA) PID that is used by the PCM as an index to look up various tables that are indexed on grams/second. This values is derived from the MAF signal.

GM.DYNCYLAIR_DMA - internal (DMA) PID that is used by the PCM as an index to look up various tables that are indexed on grams/second. This values is derived from the MAP, RPM, IAT and VE tables and is independant of the MAF.

We added the last two (DMA) PIDs because they give more accurate feedback of the indexes (indicies?) used by the PCM when looking up table values. We found that the non-DMA PIDs sometimes lagged actual operating conditions by a frame or two.

Hope that helps somewhat, and doesn't confuse the issue any further.

Oh, and about the non-functioning "More info..." on some PIDs, they are incomplete and we are still working on adding the descriptions for them.

Regards
Paul

[Extinct]

That explanation does help !

However, I am still not 100% clear on the DMA differences. For example, GM_DYNCYLAIR vs GM_DYNCYLAIR_DMA

Finally, it would seem to me that I could calibrate the MAF by mapping the DYNAIR and then pasting those values into the MAF table - is that correct ?

I did it for giggles and it looks very close to my stock curve, less a 1 g difference for most of the part throttle sections, although my engine appears to be more efficient by about 5-10 g/sec at high frequencies (rpms). BTW, I have the VE table dialed in to less than .01 BEN at said high frequencies.

[Blacky]

That explanation does help !
However, I am still not 100% clear on the DMA differences. For example, GM_DYNCYLAIR vs GM_DYNCYLAIR_DMA

They are essentially the same value. Internally the PCM keeps a value that tracks the current grams per cylinder. Assume it is called "AIRMASS". The PCM uses the value of AIRMASS (and RPM) to lookup the values in the spark table (i.e. the grams/cylinder value). When a scan tool requests "normal" PID data fromt he PCM the request goes to the PCM and the PCM looks up the value of AIRMASS, filters it (which removes spikes, but causes the value to react more slowly), formats and scales it according to what the published PID definition requires and then transmits it back to the PCM. All that"processing" can alter the value slightly - sometimes enough to make it appear to be in the neighboring cell. The DMA PIDs are the raw value directly from the PCM's "AIRMASS" variable in memory - no filtering, no formatting just raw immediate data. The DMA stands for Direct Memory Access.


Finally, it would seem to me that I could calibrate the MAF by mapping the DYNAIR and then pasting those values into the MAF table - is that correct ?

I did it for giggles and it looks very close to my stock curve, less a 1 g difference for most of the part throttle sections, although my engine appears to be more efficient by about 5-10 g/sec at high frequencies (rpms). BTW, I have the VE table dialed in to less than .01 BEN at said high frequencies.

Yes - it will be *very* close if your VE is dialled in - which yours is.

Remember that the VE will only be dialled in at the same air temp that you created it. So i fyou are doing the MAF curve make sure you do it at the same ambient air temp. Normally the STFT and LTFTs take care of air temp variations. That could be why you are seeing different flow numbers at high frequencies - when the PCM goes open loop and ignores the LTFTs.

Regards
Paul

[Extinct]

VE was dialed in on the same day and at the same time as the MAF maps, so I am confident it is not a temperature variation. Also, this was all done with the system set to open loop via the closed loop ECT table set to 250 degrees F, so it was in open loop the entire time.

Thanks for the explanation of DMA, and for providing it as a PID. I am guessing that will make our tuning more accurate by not being in the neighboring cell.

Overall, thanks for the handholding, I'm now comfortable using my map values to program a new MAF curve ! I'll report back results next spring :(