What to Tune First

[dfe1]

Following is the information supplied to me by a GM engine control specialist:
The engine control module uses a combination of the MAF
sensor and the MAP sensor to compute trapped cylinder air mass, which is
used as a critical operating parameter for much of the control system.

When the engine is in a "steady state" situation, the MAF sensor
measurement is an accurate representation of trapped cylinder air mass. A
"steady state" is defined as when actuators (such as the throttle or cam
phasing) that control air flow into or out of the manifold are not moving.
In this circumstance, the mass of air in the intake manifold is stable.

If one of those actuators is moving, it will generally cause the mass of
air in the intake manifold to change. Because of this change of air mass
in the manifold, the MAF sensor (which measures air entering the manifold)
is not correctly measuring the air in the cylinder (which is the mass of
air exiting the manifold). This transient phenomenon is called "manifold
filling (or emptying)".

During these transient maneuvers, the MAP sensor is a more accurate
representation of the state of the air entering the cylinder. Therefore, a
speed density calculation (using the MAP as its basis) is used during these
transient situations.

The only scenario where the MAP sensor is used exclusively is in case of a
MAF sensor failure.

[SSpdDmon]

Following is the information supplied to me by a GM engine control specialist:
The engine control module uses a combination of the MAF
sensor and the MAP sensor to compute trapped cylinder air mass, which is
used as a critical operating parameter for much of the control system.

When the engine is in a "steady state" situation, the MAF sensor
measurement is an accurate representation of trapped cylinder air mass. A
"steady state" is defined as when actuators (such as the throttle or cam
phasing) that control air flow into or out of the manifold are not moving.
In this circumstance, the mass of air in the intake manifold is stable.

If one of those actuators is moving, it will generally cause the mass of
air in the intake manifold to change. Because of this change of air mass
in the manifold, the MAF sensor (which measures air entering the manifold)
is not correctly measuring the air in the cylinder (which is the mass of
air exiting the manifold). This transient phenomenon is called "manifold
filling (or emptying)".

During these transient maneuvers, the MAP sensor is a more accurate
representation of the state of the air entering the cylinder. Therefore, a
speed density calculation (using the MAP as its basis) is used during these
transient situations.

The only scenario where the MAP sensor is used exclusively is in case of a
MAF sensor failure.

Based on what he's saying, it begs the question - why would we need a MAF?

[redhardsupra]

maf is way easier to tune
maf is very good at steady state
maf relies on one sensor instead of a bunch of them--more reliable

[jfpilla]

Based on what he's saying, it begs the question - why would we need a MAF?

Boring

[SSpdDmon]

maf is way easier to tune
maf is very good at steady state
maf relies on one sensor instead of a bunch of them--more reliable

Boring

eye no - just playing devils advocate.

[jfpilla]

eye no - just playing devils advocate.

I thought you were pulling our chains.

[ScarabEpic22]

No MAF for me fellas! GM designed the P10 without a MAF and still got the power and economy they needed. That said, in late 05 when they redesigned the I6 GM gave it a MAF...

[odd boy]

Is this what you're asking:

At WOT:
- the PCM calculates the airmass from the MAF (B5001),
- the PCM looks up the commanded AFR from PE (B3618),
- the PCM uses those two to calculate fuelmass,
- the PCM looks up the injector flow rate from IFR (B4001),
- the PCM uses those two to calculate the injector pulse width.

At WOT, airmass would come from B5001 since rpm is above B0120.
At WOT, PE would be enabled, and B3618 would be richer than B3605, so B3618 wins.
At WOT, MANVAC would be zero, so first cell of B4001 is the injector flow rate.

Exactly to the point, many thanks to you both Joe and jfpilla.

[BrianC98Z28]

Question.... because ive been following this thread. on my buddies 403 we put a 85mm maf on his car and I put a ls6 maf table in it and it seems to be doing WAY better than it was with a "professional" tune with the stock maf. I know 01+ Z06s came with 85mm mafs so I figured a good starting point would be the ls6 maf table. How do I go about further tuning the maf correctly to get it all dialed in because I saw there is already so MAF maps made from efilive

[TAQuickness]

Depends on your method of tuning. Per concept 1, you would use the same principles of the AutoVE tutorial and apply them to the MAF table. Per concept 2 (guys chime in if I misunderstood) you would accept your MAF table as a constant and tweak your IFR table.