Originally Posted by v8

you can just tune the maf, but if it goes bad it has nothing to go off of, unless you tune the VE as well, if your not worried about the VE table and losing the maf then just tune the maf and say done ahhaha

Originally Posted by chris@HPT

...for the most part the VE doesn't have much control when the MAF is connected, it has the ability to make a small correction to the MAF during transients (along with the change in TPS and MAP) as part of an airflow prediction calculation. If the MAF fails or gets outside calibrated boundaries (like you have a leak) then the VE table can take over completely once P101,102 or 103 are set.

Originally Posted by chris@HPT

LS1 VCM Main Airmass Calculation
The VE table looks as though it is in meters cubed; it is just not used like a conventional VE table. The VE values are such that the PCM can directly back calculate to g/cyl, the primary means to determine fueling and timing.
This is what makes it so confusing. You can't solve for air mass, you have to solve for g/cyl.
The equation
VE = ((mass flow * IAT / (MAP * RPM * Displacement))
Mass flow: grams/sec
IAT: Degrees Kelvin
MAP: Bar
RPM: RPM
Displacement: Cubic Meters

To solve for the mass flow in g/sec simply re-arrange the equation.
Mass flow = (VE * MAP * RPM * Displacement) / IAT

A very important calculation the VCM must make to ensure correct fuel mixtures under all driving conditions is the dynamic air mass calculation. This is the main calculation the VCM uses to determine how much air it should use for the Base Fuel Calculation (Inj PW). The air mass calculation is not simple and uses various combo's of MAF and SD inputs depending on engine operating conditions such as current engine RPM. It may also make decisions based on whether the engine is in a steady load state (steady MAP) or unsteady load state (Unsteady MAP). Note, that these thresholds change with RPM and MAP. E.g. at higher RPM or high MAP readings you have more leeway before the VCM decides that you have an Unsteady MAP condition. This unsteady MAP definition is basically there to decide if a throttle transient has occurred (or other) i.e. the MAF input is known not to be accurate under these operating conditions.
Under normal conditions (i.e. all sensors working properly) in the code I’m looking at it is like this:
(caveat: many of these thresholds may vary between code revs and vehicle type)
RPM > 4000
----------
trust MAF completely and ignore SD calcs (apart from MAF sanity checking purposes)

RPM < 4000
----------
if RPM < 2400 and MAP < 84 kPa then
Steady MAP threshold = 0.0 kPa
else
Steady MAP threshold = 0.8 kPa

If (Steady MAP) then
Calculate MAF Air mass/SD Air mass ratio (used for Unsteady MAP operation)
Correction Air mass = MAF Air mass (filtered)
else
Correction Air mass = SD Air mass x MAF/SD Air mass Ratio (calculated during Steady MAP conditions)

Transient Corrected Air mass = previous Final Air mass + proportion of Correction Air mass

Final Air mass = fn(MAF Airflow, previous MAF Airflow, prev 3 MAP readings, prev 3 TPS readings,
Transient Corrected Air mass)

There are 9 coefficients to this filter (and a total of up to 16 different sets of coefficients depending on operating conditions). It is worth noting that the previous value is weighted heaviest followed by the 2 MAF terms, so MAF dominates IMHO).

There are also a number of checks at the end to make sure things do not exceed certain limits.
To summarize:
1. High RPM behavior is totally based on MAF
2. Mid RPM behavior has an allowance on Steady MAP behavior before it switches to Unsteady MAP
3. Low RPM behavior (where the bulk of the fuel cells are) is dictated by unsteady MAP behavior that is still mostly dominated by the MAF input with small tweaking from SD)


If the VCM decides that a throttle transient has occurred (unsteady MAP), the airflow incorporates a "correction" from the SD calculations. This value is the SD calculated air mass multiplied by the previous ratio of measured MAF air mass to calculated SD air mass (this normalizes it, since you are worried about the transient deviation from MAF air mass only). The way I understand it is this, imagine you are cruising (MAP is steady), you have a decent vacuum in the manifold and you change the throttle position quickly. Air rushes into the manifold to service the change in air demands from the engine itself but also to try and fill the vacuum. The result is that the MAF reads higher than it should at that point in time (spikes). This is more pronounced at low RPM where the engine airflow is smaller and the relative proportion of extra airflow due to filling vacuum is higher, also the MAF is known to be more inaccurate at lower RPM and more non uniform airflow. IMHO, the SD correction is to account for filling and emptying of the manifold during throttle transients and also to smooth the MAF's spikiness at lower RPM’s.

The bottom line is that if the engine is at a steady load state or operating at high RPM then the airflow is 100% based on the MAF once you get thru all the filters and calculations. And the SD calcs only get used for transients and smoothing lower speed operation.

At no stage does the MAF get ignored completely in these calcs (the dominating terms of the main filter calc are always MAF based).

Originally Posted by BlackGMC

Dear lord Dewey, that is alot of info, I tried reading it this morning before I had my coffee and I don't think I made it threw the first few lines..... Now having reread it, it makes sense!!! Now given what all that said, seems like tuning both is needed!!! My latest tune I tuned both VE and MAF with my wideband.... I am wondering, given what was posted above if it would be a good idea to tune the VE a little richer so when a transeint condition does occur the engine has a little extra fuel, to prevent a lean spike...

Thanks again for the research...