tici

iTrader: (1)

The PCM needs G/Cyl to pick up a timing from the Timing Table (G/Cyl vs RPM).

How does the PCM determinate G/Cyl? Using the MAF? The VE table? Other ways?

What happens if I modify the MAF or the VE table?


Stefano

Shallow Bay

iTrader: (3)

Here's an explanation from EFILive.

"The air mass per cylinder can be determined from the VE table using the following formula:

g/cyl = VE*MAP/charge temperature

Ve is in g*K/kPa,
MAP is in kPa,
charge temperature is in degrees Kelvin."

ringram

MAF measures g/sec not g/cyl. But if you know the RPM and cylinder volume and the amount in air going into the engine then you can figure out the volume per cylinder on each revolution and knowing the volume with your pv=nrt kind of calc you can have g/cyl as per the efilive/GM formula posted above.

tici

iTrader: (1)

Thanks!

My MAF table is 6-7% higher than the stock values.
With the MAF connencted or in SD I see the same fuel trims which are between -2% and +2%.

This means that the PCM is taking a G/cyl 7% higher than reality?
More G/cyl means less timing advance: does it mean my engine is working with less timing than what it should?

What should I do? Keep the stock MAF table, reduce the IFR by 6-7% and reduce the VE by 6-7% too? Theoretically I should get the same fuel trims as now but the PCM would command the correct timing advance

...theoretically...

Frost

iTrader: (45)

talk about going around your elbow... why not just command the timing you WANT like everyone else?

tici

iTrader: (1)

I know the timing I need at WOT (dyno tested) but I don't have a clue about the rest, so I prefer to use the stock values.

Right now my PCM is seeing more air than reality so I guess the timing advance is not correct. Something like 1-2* less that what it should be.

Frost

iTrader: (45)

Well for that matter, who is to say it was correct from the factory Just raise most of the map and trim it back if you get KR and do the same with surrounding cells. That's about all you can do on the street.

tici

iTrader: (1)

I personally prefer the idea of "the highest power with the lowest timing".

Frost

iTrader: (45)

sounds great but you were implying that you had no dyno and no clue, so what other option do you have besides leaving it alone?