Understanding PE v. VVE v. MAF

[cscott]

When in PE mode, does the ECM solely rely on static data such as VVE table/*coefficients? I ask because I noticed the ability to define an EQ ratio, and my logs show that the commanded AFR adjusts to match the EQ ratio. That implies that some fueling adjustment happens. I've seen references to "filtered MAF", but haven't found a clear definition of the term. I also noticed short term fuel trims stop during PE.

I'm coming from the GM Gen3 world, which just jumps into the VE tables during PE.

[blindsquirrel]

PE is a multiplier of whatever is in the VE - same for VVE. Your Gen 3 was doing that as well, they do not just revert to open loop and use whatever is in the VE.

I think the correct term is 'filtered airmass', which is a blend of MAF and VE/VVE using a bunch of math stuff, depending on conditions. If somebody called it 'filtered MAF' I think that was just a typo or other misunderstanding.

[cscott]

PE is a multiplier of whatever is in the VE - same for VVE. Your Gen 3 was doing that as well, they do not just revert to open loop and use whatever is in the VE.

I think the correct term is 'filtered airmass', which is a blend of MAF and VE/VVE using a bunch of math stuff, depending on conditions. If somebody called it 'filtered MAF' I think that was just a typo or other misunderstanding.

Got it. Thanks a lot.

[Cringer]

When in PE mode, does the ECM solely rely on static data such as VVE table/*coefficients? I ask because I noticed the ability to define an EQ ratio, and my logs show that the commanded AFR adjusts to match the EQ ratio. That implies that some fueling adjustment happens. I've seen references to "filtered MAF", but haven't found a clear definition of the term. I also noticed short term fuel trims stop during PE.

I'm coming from the GM Gen3 world, which just jumps into the VE tables during PE.

The ECM LOVES to use the MAF (aka filtered airmass) for its primary source of determining airmass because it is so accurate. The VVE (aka dynamic airflow) table is really only used for reference for transient fueling (when you are opening and closing the throttle since the MAF is slow to respond quickly to changing air mass). Steady state throttle and WOT all goes back to MAF as the primary determination of airmass.

The reality is that the ECM looks at both MAF and VVE to get an idea on what the airflow is and factors in running conditions and atmospheric conditions to make a decision on what is the most appropriate airmass...this would be the dynamic airflow. Sometimes the ECM weights the MAF input more, sometimes VVE more, but it always blends them to some extent. You can log the MAF, VE, and dynamic airflow in the scanner to get an idea on what is going on with this relationship.

Also, during PE the narrowband O2 sensors are useless (they can only be used for stoich reporting). As soon as you go rich in PE, the narrowbands are ignored, and as such the STFT also go to 0. At this time, the car is blindly going off the dynamic airflow it has calculated. This is why you need a wideband, so you can dial in the airflow model during PE.

[ttz06vette]

The ECM LOVES to use the MAF (aka filtered airmass) for its primary source of determining airmass because it is so accurate. The VVE (aka dynamic airflow) table is really only used for reference for transient fueling (when you are opening and closing the throttle since the MAF is slow to respond quickly to changing air mass). Steady state throttle and WOT all goes back to MAF as the primary determination of airmass.

The reality is that the ECM looks at both MAF and VVE to get an idea on what the airflow is and factors in running conditions and atmospheric conditions to make a decision on what is the most appropriate airmass...this would be the dynamic airflow. Sometimes the ECM weights the MAF input more, sometimes VVE more, but it always blends them to some extent. You can log the MAF, VE, and dynamic airflow in the scanner to get an idea on what is going on with this relationship.

Also, during PE the narrowband O2 sensors are useless (they can only be used for stoich reporting). As soon as you go rich in PE, the narrowbands are ignored, and as such the STFT also go to 0. At this time, the car is blindly going off the dynamic airflow it has calculated. This is why you need a wideband, so you can dial in the airflow model during PE.

Is MAF always interpolated in the background no matter what RPM you enable it at in the tune?

[Cringer]

Is MAF always interpolated in the background no matter what RPM you enable it at in the tune?

I am assuming you are referring to these two tables:
[ECM] 3003 - Dynamic Airflow High RPM Disable
[ECM] 3033 - Dynamic Airflow High RPM Re-Enable

And the answer is YES, the MAF is always in play. These tables help to define the threshold for the weighting algorithm between the MAF and VVE inputs which determines the dynamic airflow. So if you move the RPM's higher, it adds weight to the VVE input, if you lower them it adds weight to the MAF input. I don't know the exact algorithm behind the scenes though, but merely moving the RPM's to the max will still allow the ECM to utilize the MAF to some extent.

The only way to take the MAF out of the equation is to fail it using the parameters defined in ENGINE DIAGNOSTICS > AIRFLOW > MASS AIRFLOW SENSOR. Or I guess you could unplug it too...

As far as I know there is no way to disable the VVE input.

[blindsquirrel]

I found that my MAF works best when stored in the junk box under my workbench.

[ttz06vette]

Thanks for the response. “Yes” I was referring to the dynamic airflow tables. Good to know I need to go back and make sure my MAF trims/ frequency are still good below the 2500rpm threshold I have dynamic air set at. I have not been looking at them and only focusing on VE below that RPM. Clearly the algorithm works though, as I have been able to tune out a lot of bucking and off idle bog through VE once I raised dynamic air enable above the threshold it was happening at. I believe it was due to turbulence in the airstream caused by the intercooler piping design I have in front of the MAF.
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