A little help with VVE tuning

[clinter36]

2011 Silverado HD, 6.0, E78 ECM

Without going into details, this truck has never run quite right... hesitation, bucking, etc. I have been reading/learning and scanning for over a year (made some easy transmission changes, etc). Finally I have some time to get this engine sorted out.

I am tuning VVE with fuel trims - yes I will get a wideband and re-tune VVE as well as the MAF, but for now I am going to use the tools I have on hand (I still have a lot of learning to do).

Here are my problems...

1) VVE table uses MAP / Baro. I tried using Math>pressure ratio on the scanner, but I don't get any data. So I used MAP and the same break points but scaled up x100 (for example for .13 on the MAP/Baro I used 13 MAP) assuming BARO is around 100, this should at least get me close. Is there a better solution here ??

2) Despite 9 + attempts at modifying the VVE, My fuel trims seem to get worse. My understanding is that I am supposed to add the values from the histogram (or whatever we call that now) directly to the VVE table, until I get my fuel trims close, then I use "multiply % - half". The more I think about this, the more I confuse myself.... Fuel trims are in percent, but the table displays whole numbers (-1, 5, 11,.... so one). Percents are typically multiplied... So if my fuel trim was -5, I want to adjust my VVE cell down by 5%. If I add to the VVE table, am I adding -5 or adding -.05 (not sure which) neither gets me where I want to go. I did try multiplying and have not seen much improvement. Can someone please explain this a little better for me...?

FWIW, what I am trying to tune out significant bucking felt under load and RPMs 1400 - 2000. when I feel the bucking I can see my STFT go from 10 positive to -10 (ish) and it seems to correspond with the bucking. Taking MAF out of the loop as certainly changed things and the bucking has gotten better and worse with various iterations of my attempt at tuning VVE.

Thanks for all your help!

[crutt]

1. VVE- you want to set the parameter as ltft+stft under maths, column as rpm and rows as kPa from the MAP sensor. Copy your axis' labels. Log.

2. Do not add/subtract the values! As these are a percentage, copy your graph, and multiply your vve table by half, then apply the coefficient. You might need to do this in both vve tables. You might have to hand smooth.

I've attached my graph setup.

Untitled.png

IF YOURE DOING VVE REMEMBER TO FAIL THE MAF

[clinter36]

Thank you...

I did answer some of my own questions. Math>pressure ratio wasn't logging because I was not logging Barometer in the PIDs. With that added, I now have a working fuel trim histogram that matches the VVE table.

I am currently logging just short term fuel trim with LTFT turned off. I would think that is very close to logging both LTFT and STFT combined, but I suppose there could be some nuances. I'll run a fresh session with combined fuel trims to see how close she looks.

After a couple of logging sessions last night and using "multiply %" to bring the data over to the VVE table, I am now logging STFT that are mostly between 0 to -2 with the exception of a few regions. So we are making progress! I will also mention that the bucking is drastically better.

I am not sure I follow your suggestion to multiply the VVE table by 1/2 then apply the coefficients.... But I think since I seem to be close in many regions, I am going to work with the VVE in small sections and leave the entire table alone. Maybe even RPM column by column.

Here is a general Volumetric Efficiency question that maybe someone can shed a little light on... There are dips and valleys in the VE table as a result of varying efficiencies in the pressure, flow (rpm) matrix (how much air actually gets into the cylinder at a given RPM/pressure). No doubt due to Bernoulli's principle in some way or form. Is the efficiency most likely to stay consistent (smooth) across the RPM column or the pressure row? In other words, am I better off smoothing things out along a RPM column or a pressure row ??

[Brettworth]

I need to do this to my truck, this sounds really bad, but where is the table to change in the GEN4? I've logged longterm+short term and also have a wideband. I've used them to fine tune the MAF, but now want to change the base VE for speed density tuning. I know to fail the MAF and all, but just can't figure out where the tables are I need to change.

Thank you ahead of time

[johnny_boii]

Open the tune file and in the top left corner click edit and then you will see virtual volumetric efficiency. Most people will recommend you using your wideband if you have it setup correctly. You can disable the fuel trims with the scanner tools

[Lakegoat]

VVE Tables are under Edit---Virtual Volumetric Efficiency. Click on the closed button and two others open.

[clinter36]

I need to do this to my truck, this sounds really bad, but where is the table to change in the GEN4? I've logged longterm+short term and also have a wideband. I've used them to fine tune the MAF, but now want to change the base VE for speed density tuning. I know to fail the MAF and all, but just can't figure out where the tables are I need to change.

Thank you ahead of time

After you correct the VVE table (under "Edit" as pointed out). You then need to do whatever smoothing, then click "Calculate coefficients" and that box will go grey (unavailable). You will also notice there is a drop down box at the left for "manifold switch closed" "manifold switch open" "Manifold DOD". Once you have the first table how you want it, you will need to copy the table for the other manifold options. There is scattered info on which table is used.... I don't have DoD so I didn't need to mess with the two DoD tables, but I made both switch open and closed tables the same. This was one of the original problems I was having because I don't think the VVE table I was adjusting was being used.

[Brettworth]

Sweet! Thanks guys!

[RySmDPT14]

I have tuned my e78 multiple times after my VVT cam install, intake and exhaust. Surprising to know that the VE table is affected with these changes. I logged LTFT + STFT until my LTFT were within +- 2. I attempted to log just my STFT and I was getting so much variability that i was just going in circles, when you get close to good numbers multiply your fuel trims by half when adjusting the VE table, so you don't overshoot and run in circles...

[clinter36]

After I got close I have been using multiply % - half. I still feel like I am running in circles !

[RySmDPT14]

How do your LTFt look? If they are solid then I would go with what you have. STFT are immediate changes that will be different based on driving technique, I looked at mine yesterday and they changed from Drive to drive when I Log. From what I read stft+ltft math is used to tune these days and not just stft because of the variability of stft.