Help Interpreting GMVE Results - e40 ECU

[Dave_In_VA]

Trying to finish tune of mildly camed / built LS2 with LS3 top end.

I tuned MAF and VE tables pretty close, more or less plus minus 1 (or so%) for both tables. PE is set at 13:1 with delay at 3500 RPM, but WOT PE is set to 40% at 3K and 20% at 4K.

High MAF tables have been adjusted to get WOT AFR in the 12:5 to 12:9 range. A dyno session later this fall will fine tune WOT AFR and other parameters. My wideband reads pretty consistent mid 14s:1 on all of my tune drives unless PE is active. So the car is pretty happy fuel wise.

STFT is on, LTFT and DFCO is off.

Here's my quandary. I noticed that when trying to fine tune GMVE STFT I was eliminating all large % errors (both positive and minus) but my STFTs were consistently running about 5% lean across the board below 4K RPM.

So I said ok, lets see if I can minimize STFTs and I added 5% fuel to all cells 4K below, a little less above 4K. A couple of refining tune drives resulted in this STFT graph: Screenshot 2022-06-22 080558.png

However, now my STFT GMVE log file is running really rich, see: Screenshot 2022-06-22 080629.png

So I'm totally confused. If my MAF tune is pretty good, and using GMVE my VE values are pretty good, shouldn't my STFTs be minimized.

What am I missing?

[Lakegoat]

Turn off your MAF when tuning VE. Engine Diagnostics--Airflow--Fail high (1), Reenable(0). DTC's---P0101,102,103--Mil on first error, Engine Airflow---Dynamic---8000rpm/7900rpm. Then tune the VE. You are not in SD

[Dave_In_VA]

I thought the entire purpose of GMVE tuning is you don't need to be in a dedicated SD mode?

Also, what is the relationship between GMVE VE error values and STFT error values. Shouldn't these two be pretty close?

Dave

[eXo3901]

Yes.

They are different error corrections. You are essentially tuning your MAF and correcting your VE table to the corrected MAF value. Re-read the MAF/VVE thread.

[Dave_In_VA]

eXo, this one: https://forum.hptuners.com/showthrea...ation-for-gen4

[eXo3901]

Yes. This snippet below clarifies it a bit, at least for me it does. You would correct your MAF by the 4.4% STFT error. But the Math parameter already corrects for that 4.4% MAF error and compares it to the GMVE lookup to get the .3% error. So no VE table correction is needed at that specific point.

To help visualize even more, you can plot MAF_af, Dynamic_af, and GMVE_af(from the thread, the GMVE conversion to airflow) on a single chart with the same upper and lower bounds and the same units. They should all overlap nicely and follow the same general flow up and down. You can even see the MAF spikes on tip in or starting off at a stop sign and watch dynamic_af ignore the MAF for a second or two and follow the GMVE_af.

Screen capture of the parameter working...

Attachment 101145

Notice at the cursor point, the average STFT in the third graph is showing -4.4%, so a MAF airflow overestimation. However the GMVE airflow, being slightly lower is showing only 0.3% error, so it's right on for that operating point.

[smokeshow]

You can even see the MAF spikes on tip in or starting off at a stop sign and watch dynamic_af ignore the MAF for a second or two and follow the GMVE_af.

Seeing that in action always turns me on in the wierdest way.

[Alvin]

I thought the entire purpose of GMVE tuning is you don't need to be in a dedicated SD mode?

Also, what is the relationship between GMVE VE error values and STFT error values. Shouldn't these two be pretty close?

Dave

This method works reasonably OK but it is not nearly as good as setting the car in a MAF failed state, doing VVE, and reenabling the MAF if you so wish. The MAF is going to be a dirty signal with reversion from the cam, sensor fouling, air dynamics in your aftermarket CAI, transients, etc..

I would save that type of VVE tuning for cars that flat out cannot run with a failed MAF.. (later LT4's come to mind)

[eXo3901]

Seeing that in action always turns me on in the wierdest way.

Lol whatever works, works.

[smokeshow]

This method works reasonably OK but it is not nearly as good as setting the car in a MAF failed state, doing VVE, and reenabling the MAF if you so wish. The MAF is going to be a dirty signal with reversion from the cam, sensor fouling, air dynamics in your aftermarket CAI, transients, etc..

I would save that type of VVE tuning for cars that flat out cannot run with a failed MAF.. (later LT4's come to mind)

I did include explicit instruction in the original post addressing that caveat directly. Fueling error data collected duringany transient operation precludes airflow model calibration with that data, period...speed density or otherwise. A good set of filters and a watchful eye goes a long way.

One thing to remember, as you always should when calibrating anything airflow related...it must be at steady state. So you should be using a method of your choosing to filter out transients

[Dave_In_VA]

Yes. This snippet below clarifies it a bit, at least for me it does. You would correct your MAF by the 4.4% STFT error. But the Math parameter already corrects for that 4.4% MAF error and compares it to the GMVE lookup to get the .3% error. So no VE table correction is needed at that specific point.

To help visualize even more, you can plot MAF_af, Dynamic_af, and GMVE_af(from the thread, the GMVE conversion to airflow) on a single chart with the same upper and lower bounds and the same units. They should all overlap nicely and follow the same general flow up and down. You can even see the MAF spikes on tip in or starting off at a stop sign and watch dynamic_af ignore the MAF for a second or two and follow the GMVE_af.

eXo, I'm working on the GMVE_AF from the other thread, see below. MAF and Dynamic were easy.

GMVE_af = (MAP*GMVE/IAT)*RPM/60*4

Take MAP in MEGApascals (important) and multiple by the raw GMVE value from CAN and divide by the IAT in KELVIN (also important). This gives a single cylinder airmass. To get flow rate, multiply by RPM, divide by 60 to get revolutions per second, and multiply by 4 for the number of induction cycles in one revolution. If you have a 4 or 6 cylinder, multiply by 2 or 3, respectively.

So I'm creating a custom formula for GMVE_AF. When trying to add the GMVE variable nothing comes up. This is my formula so far - question marks are where the GMVE parameter should go: 2022-06-25 (5).png

Per the above: "multiple by the raw GMVE value from CAN"

What is CAN?

BTW, I'm using MAT instead of IAT in this formula.

[LS ROB]

Per the Acronym list: CAN-Controller Area Network

I pulled that from the acronym list, so, if it's different from that, my apologies.


https://forum.hptuners.com/showthrea...2-Acronym-List

[eXo3901]

There are 2 VE PIDs you can log. One is an airflow and one is the raw GMVE value from your VE table. The airflow value is (I believe) calculated directly from the looked up GMVE value from your VE table. You will use the raw GMVE value in that GMVE_af math. It will report in (kg/mg..something). The benefit, described in the thread, is that using the raw value avoids the 512g/s airflow limit. If you are nowhere close to that, I guess the VE airflow pid should work but you need to change the math.

[Dave_In_VA]

All, many thanks to all that helped with my tune.

Sunday I spent a very hot afternoon finishing my tune via some dyno time.

Shouts out to Landon at Elite Speed (https://elite-speed.com/)

Car made 471 RWHP and 445 torque, and the torque was 400 plus from 3000 PRM to redline.

AFT at WOT targets 12.7:1 and its really close to that, s/b a nice safe tune. No knock. Tuner said my dynamic efficiency was 97%. He indicated that he thinks my throttle body is limiting output a little.

The car is very drivable from 1000 RPM up, but if slowing down in a higher gear around 1000 RPM it bucks some. But it is a cammed car and thats to be expected some. I have a little fine tuning to do, but very little.


See: Fraley Tune - June 26 2022.png


thanks everybody....