PID confusion

[redhardsupra]

I love variety, but sometimes it gets confusing with all these PIDs. What's the difference between:

GM.DYNCYL_AIR_DMA
GM.DYNCYL_AIR
GM.CYLAIR_DMA
CALC.CYLAIR

or

GM.CHRGTEMP_DMA
GM.DYNAIRTMP_DMA
GM.IAT

or

GM.MAF
SAE.MAF

any tutorials on that? :notacrook:

[ringram]

Stop asking complicated questions :)

[redhardsupra]

Fine, I'll ask something easier:
1. Could we get an abstracted AIRFLOW value, so it doesnt' matter whether I'm going off VE/SD or MAF?

2. Is it possible to increase the resolution of DynCylAir, since it's the closest thing we got to compression/torque sensor?

Easy enough? ;)

[Dirk Diggler]

GM.DYNCYL_AIR_DMA - PCM Calculated air in SD mode
GM.DYNCYL_AIR - A prediction most likeyl based off of map, maf, iat and ect
GM.CYLAIR_DMA - PCM Calculated air in MAF mode
CALC.CYLAIR - Calculated gms/cyl for spark tables and such based of of the air read from the MAF sensor

GM.MAF and SAE.MAF are the same things Paul may be able to elaborate more.

GM pids are LS1 specific (I read that somewhere) SAE Pids are generic and work on most OBD2 vehicles like 95-97 LT1's

[joecar]

I got this from Paul quite a while back...



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.

[dc_justin]

I got this from Paul quite a while back...

Good to know, as I have seen some large discrepancies between GM.MAF and SAE.MAF. :cheers:

[blandmiller]

Does anyone know if the GM.DYNCYL_DMA works for vehicles that do not have a MAF from the factory? The LL8 PCMs run in SD only and I can't seem to get any airflow values to make sense.

[SSpdDmon]

I always went by the rule that the table in the tuning software has all the info needed for logging. Take for example the high octane spark table. The numbers in each cell are obviously degrees spark advance as indicated by the Units box on the top right next to the min and max values you can enter. Then, the table says it uses SAE.RPM and GM.DYNCYLAIR_DMA for the rows and columns. Now that you know what PIDs are used for the rows/columns, you just have to replicate that table in the scanner, select those pids along with a data PID (i.e. knock retard) and go log.