Desired Airflow Question, not your normal question

[macca_779]

If you were sticking with a MAF system rather than scale the MAF table what would happen if you adjusted the VE table?

it will effect fueling where MAF and MAP are blended but will have no effect above the default 4000rpm that is exclusive MAF fueling.

[stigmundfreud]

it will effect fueling where MAF and MAP are blended but will have no effect above the default 4000rpm that is exclusive MAF fueling.

so under 4k you could adjust the ve and above 4000 adjust the scaling. Of course that could lead to a jump around 4k+.

Its more for a case of the VE is dialed in now and the MAF scaled but to fine tune with the 2 was just wondering about the effect adjusting the ve would be

[5.7ute]

RAFIG- Running Air Flow In Gear is the sum of long term and short term idle air correction. So in a sense, it is the difference between desired and actual air flow because if they were equal, there would be no correction. The PCM uses a variety of tables to determine the amount of air correction required, but the intent of using RAFIG data is to establish desired air flow data that minimizes the amount of correction required. As you alter desired air flow table data, RAFIG numbers will change to reflect those alterations. As an example, if RAFIG is positive and you increase the desired air flow numbers, the RAFIG values will become less positive or negative, depending on the amount you increased the desired air flow numbers.

I think all this makes sense, but as Joecar said, "I forgot what the original question was...?"

The question is what sensors are used in the rafig process to determine desired airflow.
Lets get this right. Maf or Speed density has no relation at all to this calculation. it is a difference to actual & desired idle speed & nothing else.

[dfe1]

The question is what sensors are used in the rafig process to determine desired airflow. Lets get this right. Maf or Speed density has no relation at all to this calculation. it is a difference to actual & desired idle speed & nothing else.

I think there's more confusion here than anything else. When you go thorugh the RAFIG process, what you're trying to do is establish the proper desired air flow for the specified desired idle speed. If you look at the RAFIG PID, you'll see that it is simply the sum of long and short term idle air correction. If desired air flow data was perfectly correlated to desired idle speed, RAFIG would equal zero because both long term and short term IAC correction would be zero.

[bink]

The VE table's "real" units are g*K/kPa

where:
g is grams (mass)
K is degrees Kelvin (temperature)
kPa is kilopascals (pressure)

so each VE table cell value is the "normalized" cylinder airmass...
i.e. "normalized" for absolute termperature and absolute pressure;

as temperature goes down, airmass goes up (i.e. mass varies "per" 1/K),
as pressure goes up, airmass goes up (i.e. mass varies "per" kPa),
so the units are: g /(1/K) /kPa == g/(kPa/K) == g*K/kPa.

to calculate the cylinder airmass, the PCM reads the VE table cell value and divides by the absolute temperature and multiplies by the absolute pressure;

e.g.
very simplistically, say:
- PCM computues (via IAT/ECT blending) the dynamic air temp to be 300K (27°C, 80°F),
- VE table says 2.0 g*K/kPa,
- MAP is 100 kPa,
then airmass = 2.0[g*K/kPa] / 300[K] * 100[kPa] = 0.6667[g]

(note how the units balance out)

Can you organize a this info!

[joecar]

Hey Joel, how you doing

Ok, thanks, I added this to the following thread: showthread.php?14188-Summary-Notes

[ one day I'll organize all the info ]