Logging Knock Retard In Graph

[TAPyvehc93]

Which parameter do I use for the row axi? Its labeled as spark air mass in my editor but I can only find cylinder air mass for the graph parameter in the scanner.

[jtrosky]

Spark airmass and Cylinder airmass are the same thing. No idea why the names are inconsistent like that - it seems to have started in the 3.x releases.

[mowton]

I always log Dynamic Airflow and develop a user defined cylinder airmass from it as it represents the PCM's final answer in its airflow model. Just copy the MAF cylinder airmass pre-configured to an available User Defined math slot and replace the MAF parameter with the Dynamic Airflow parameter. Change the row axis on each of your Spark related graphs.

Ed M

[TAPyvehc93]

I always log Dynamic Airflow and develop a user defined cylinder airmass from it as it represents the PCM's final answer in its airflow model. Just copy the MAF cylinder airmass pre-configured to an available User Defined math slot and replace the MAF parameter with the Dynamic Airflow parameter. Change the row axis on each of your Spark related graphs.

Ed M

I am pretty new to this so I don't totally understand what you are saying here. Can you break that down a little bit more for me? Any reason I cant just use cylinder airmass like jtrosky said?

[jtrosky]

I'd like to understand this a little better myself - I've seen this mentioned multiple times now.... I've always just used the Cylinder Airmass PID that's "built in" - simply because that is how the scanner software comes configured (charts/graphs are configured to use the cylinder airmass PID by default). Plus, that one single PID seems more "universal" as it works with 4, 6 and 8 cylinder engines (whereas when defining it as a math parameter, you have to specify 4, 6 or 8 cylinder in order for the math parameter to work properly).

Just trying to understand the recommendation a little better and why it's preferred.

Thanks.

[mowton]

Dynamic Airflow is the final calculated airflow value from either the MAF or VE after all filtering applied during transient events so it basically tracks the MAF/VE airflow very closely during steady state cruising, but diverges during pedal stabs/releases to compensate for the intake manifold induced variances due to the dynamics of air. We say that the manifold is like a sponge or a spring...during transient scenario's, the airflow being reported by the MAF will either be too high (pedal stomp) or too low (hard decel). The only accurate fueling model at that time is the VE which has been painstakingly developed over thousands of hours of bench testing so it is used to filter the MAF data. Dynamic Airflow will be lower and higher than the MAF airflow at times so it wold also hold true that the MAF generated cylinder airmass would be wrong as well....

So the solution is to generate the cylinder airmass value from the Dynamic Airflow instead of the MAF airflow. So we add Dynamic Airflow to our Channels and we copy the MAF expression to the open user defined slot and change the MAF parameter to Dynamic airflow......see MAF and DC .png below...



Once complete, here is an example of the MAV vs Dynamic Airflow and resultant cylinder charge parameters. In this example if you weren't logging Dyn Air and DCA, you would think the knock you saw was based on timing in 4400/4800 rpm and .0616 g/cyl or 13.5 degrees?????? So why doe the scanner say 24? because the MAF airflow and its related Cylinder airmass parameters have not been corrected and are no longer accurate. See the last attachment.



Hope this helps

Ed M

[jtrosky]

Thanks for the detailed description. If this is the case, you'd think that HPTuners folks would default to using DCA instead of the Cylinder Airmass PID in the default scanner setups. Or maybe they can't simply because the DCA Math parameter is dependent on the number of cylinders (there is no one DCA parameter that would work with all engines).

Out of curiosity, I'm going to start logging both Cylinder Airmass (PID) and the DCA Math parameter - just to see how different they are - and how often they are different.

Thanks again for the detailed description.

[smcstevesmc]

Awesome, great information. When tuning maf, would it make sense to use the dynamic airflow?