Question regarding a logged parameter

[Enki]

So I finally noticed something that had been staring me in the face since I started my tuning adventure those many years ago.

I was comparing some logs from similar tunes and noticed that boost, MAF voltage, mass airflow, boost, timing, etc were all extremely close, but the boost temps, calculated load, IDC and VDyno output are way, way different.

This leads me to believe that the mass airflow reading that gets logged is actually just a lookup from the MAF table and *NOT* the baro/temp corrected *actual* airflow that the engine sees.

While I can provide logs if needed, I'm thinking that this is something that can only be confirmed/denied by Cobb directly, since only they will be able to dig through the rats nest that is our ECU and determine if this is the case or not.

As a side note, if it matters, I drive a 2009 first gen MS3.

[udntknw]

Not to question you, but isn't that the point of the maf scale? When the maf sees x voltage, its assumed based on the maf scale that's what the airflow is?
Or maybe I'm not picking up what you are putting down. (more likely)

Just tapa it in.

[Enki]

Basically, if you are looking at MAF voltage, you should be able to just go to ATR and translate that back into a whole number, give or take; voltage is a real, measurable number, but having mass airflow just look back to the MAF table is almost pointless if the *true* airflow number is, in fact, different from what the engine is actually basing its calculations off of.

The reason this could be important is that load numbers are at least partially based off of actual airflow; if you recall the post I made in your thread with links to the actual math used for the load PID, you'd see that there's multiple steps including factoring in barometric pressure and temperature that needs to be done to factor load.

Basically, knowing that this number is/is not accurate can make setting up a base map for load tuning quite a bit easier, and would potentially drastically improve tuning for aux fueling during weather changes (though I've not looked into that much, since I have little interest in going 5th port).

[Enki]

Just went back through the logs in question, only this time instead of comparing voltage/airflow numbers between the logs, I compared the same voltage/airflow numbers within the same log...and now I'm a bit more confused as I'm seeing the airflow climb at the same voltage in proportion to RPM, except in instances where the voltage goes up and the airflow goes down.

After doing more math from the two logs, I'm still unsure as to whether or not this is what it should be (the diff numbers are just divided by the preceding numbers both ways):

5k airflow: 5650 l/min diff: 83.33% 6k airflow: 6780 l/min diff: 120.00% ve 5k @ 2.0 load: .8660 ve 6k @ 2.0 load: .8630 eff 5k: 4893 l/m diff: 83.62% eff 6k: 5851 l/m diff: 119.57% massflow 5k: 318.02 diff: 81.88% massflow 6k: 388.38 diff: 122.12% massflow 5k: 297.32 diff: 83.18% massflow 6k: 357.43 diff: 120.21%

So basically, all else being equal, the difference in airflow between 5k and 6k rpm should be ~20% more @6k compared to 5k, and that seems to bear out in the logs; however, the difference in peak airflow before redline is only ~14 g/s and the difference in reported power by VDyno is > 50 horse.


Someone call me a cab and get me out of crazy town. Please.

[Enki]

Basically zero response on this thread/issue. Did some log tshooting with another member ( @NCspecV81; ) who was having issues with fuel pressure dropping even though he only had 80% IDCs, and it was determined that he was running out of fuel. Leaning him out resulted, strangely, in *HIGHER* IDCs and a resolution to the pressure dropping.

More fuel for the fire regarding pids that give weird/incorrect data.

[Evan@COBB]

I'll put it on the list to investigate. However, just a warning, it's a long list!

[Enki]

Better than nothing. Thanks!

[Sergeant_M]

You should just go work for NASA or something.

[NCspecV81]

This would be awesome. Something just isn't jiving right with IDC values on my logs.