VE tuned to 13.0 in WB SD, why not 14.68?

[NewVetteTuner]

I have been having some debate with my tuner about SD mode and the various idiosyncrasies involved. We initially had some hot start issues and some cruise control effect at low rpm as well as bucking on decel. While investigating this issue myself I noticed my LTFT's were not in line with the various write ups on SD tuning (out by +20% or so). The tuner did use the wideband method which sets the VE to 13.0 (he used 13.5 but I don’t think that is relevant). So I started to tune with the narrow band method and my VE table and his are VERY different. I think this is because I am tuning the VE to 14.68:1 and he did 13.5:1.
Ok, this all being said, isn't the whole point of SD to take more control over the engine and rely less on the various sensors and adaptive strategies? Would it not make sense to scale the VE table back to what it would be at 14.68:1? Am I missing something here? What would the disadvantages of scaling the VE be?

On a separate subject...
My tuner and I also had some debate about KR. The tuner has zeroed out the 'Base Retard VS RPM' table effectively neutering the KR as I read it. The other changes in spark retard included 'Maximum knock Retard VS MAP no PE' to '24' after 400 rpm and 'Maximum knock Retard VS MAP in PE' to '25 after 800 rpm. He told me that the KR was handled differently when in SD mode. Here is a snippet from that conversation.
ME: The KR tables make perfect sense to me. You are correct that the engine will make less power, since it will pull timing when it sensed knock.
TUNER: (a lot more to it than this. This is what I mean when I say some of the changes I made to various KR tables won’t make sense).
ME: I was unable to verify your explanation of KR being different in SD mode vs. MAF mode and frankly it doesn't make a bit of sense
TUNER: (I know, but you’ll have to trust me if you want to make bigger power without sacrificing KR function).
If my tuner is correct could someone explain this to me? This forum has been a pretty good resource, I really appreciate all the good information here!

[Chris@HPTuners]

I have been having some debate with my tuner about SD mode and the various idiosyncrasies involved. We initially had some hot start issues and some cruise control effect at low rpm as well as bucking on decel. While investigating this issue myself I noticed my LTFT's were not in line with the various write ups on SD tuning (out by +20% or so). The tuner did use the wideband method which sets the VE to 13.0 (he used 13.5 but I don’t think that is relevant). So I started to tune with the narrow band method and my VE table and his are VERY different. I think this is because I am tuning the VE to 14.68:1 and he did 13.5:1.
Ok, this all being said, isn't the whole point of SD to take more control over the engine and rely less on the various sensors and adaptive strategies? Would it not make sense to scale the VE table back to what it would be at 14.68:1? Am I missing something here? What would the disadvantages of scaling the VE be?

On a separate subject...
My tuner and I also had some debate about KR. The tuner has zeroed out the 'Base Retard VS RPM' table effectively neutering the KR as I read it. The other changes in spark retard included 'Maximum knock Retard VS MAP no PE' to '24' after 400 rpm and 'Maximum knock Retard VS MAP in PE' to '25 after 800 rpm. He told me that the KR was handled differently when in SD mode. Here is a snippet from that conversation.
ME: The KR tables make perfect sense to me. You are correct that the engine will make less power, since it will pull timing when it sensed knock.
TUNER: (a lot more to it than this. This is what I mean when I say some of the changes I made to various KR tables won’t make sense).
ME: I was unable to verify your explanation of KR being different in SD mode vs. MAF mode and frankly it doesn't make a bit of sense
TUNER: (I know, but you’ll have to trust me if you want to make bigger power without sacrificing KR function).
If my tuner is correct could someone explain this to me? This forum has been a pretty good resource, I really appreciate all the good information here!

Max retard in PE and not in PE are maximum KR values setting them to 24 or whatever is kinda strange, who wants the PCM to retard the timing by up to 24 degrees?

Anyone who completely deactivates KR on a street tune needs to think about why they are doing that, since the engine has knock sensors it's probably a good idea to use them.

KR is handled no differently in SD or MAF mode, what is different is that the knock learn factor (octane scaler) fully maxes out to the low octane table.

When you start an SD tune using a WBO2 (ie. trying to align your commanded AFR to the measured AFR) you must make sure the LTFT's and STFT's are disabled and reading 0 in the scanner at all times.

The idea of SD is to manually provide the PCM with the airflow information it would usually receive directly from the MAF. In some cases SD has obvious benefits such as reduced intake restriction, freedom of intake structures (eg. 8 TB setups) etc. Apart from that unless this is a racecar i wouldn't want to lose any features.

[ramjudd]

Chris;

could you clarify/reiterate how to disable the trims?

could you also be a little more specific about the initial VE table tuning regarding how we aim to tune it to 13.0:1 with wide band, just as the procedure indicates? This post is asking why would we choose to set the Open Loop to an AFR setpoint of 13.0 then tune the VE with Wide band to achieve this in all cells when the narrow band instructions actually have you tuning the VE table via trims to stoic? With everything else being the same supposedly, the car ran like crap with the VE tuned to 13.0 (then closed loop re-enabled). But when the same car VE table was tuned by narrow band method by achieving 0 trims (VE table = stoic?), the car ran great.

[NewVetteTuner]

Chris, thank you for replying, and damn quick too! Do you have any thoughts on the 13.0/14.68 portion of my post? I am VERY curious to see what others have to say on this issue. I did do some searching but was not able to get any good answers. As I said, it seems to me that we want the VE table to be as close to stoic as possible to minimize the amount of correction needed to get us to 14.68:1. Since we have to use the WBo2 o tune PE anyway, is there a downside to what I am proposing?

Thanks guys!

[Bill@HPTuners]

I always understood it as because of you trying to hit as many cells as possible without going wot theres still a possiblity of you going into an area of cells that would've put you in pe mode under normal accelleration and therefore a commanded afr of 13.0:1 is just to keep things safe...remember just because your commanding 14.68 doesnt mean it will hit it...you could hit 15.5 at some of the higher cells & if you werent keeping a close look at that could damage something pretty easily.

[Chris@HPTuners]

I usually just disable fuel trims/closed loop and go slow near the transition to PE so i don't mistakenly tune to the transient. So i tune to both 14.7 and whatever i want my PE ratio to be. However, i do all my tuning on the dyno where it's a lot easier to control things.

you need to be certain that your commanded AFR is what you expect it to be and also be certain all of your fuel trims are 0 during the process.

To disable your fuel trims set your closed loop enable temp to something very high. Beware, i have seen some 1Mb calibrations that still allow the STFT's to function even when you do this. I haven't investigated this fully but you can disable them all by using the VCM Controls in the scanner. Also, reset your trims to 0 using the reset fuel trims control.

I always use the AFR % Error histogram when tuning and once completed i turn closed loop back on again and see where the trims end up, usually they are right around 0. If you want to get really precise you could tweak the rich/lean voltages to give you slightly negative trims if you are concerned about it.

I can't think of any other reason you would see such a difference when you turn closed loop back on regardless of what AFR you tune to (its quite a linear process). Assuming your timing isn't extremely retarded during the process.

[NewVetteTuner]

"I can't think of any other reason you would see such a difference when you turn closed loop back on regardless of what AFR you tune to (its quite a linear process). Assuming your timing isn't extremely retarded during the process. "

Is this to say that the VE table should end up the same with open loop commanded 13:1 as 14.7:1? It seems to me like it would be 13% off causeing my trims to have to compensate for this 13% difference based on the os'2 input. My tuners VE coincidently is about 10% higher than mine, he used the WBo2 method.
Maybe I am overemphasising the importance of an accurate VE table and the trims don't care about 13% difference?

[12secSS]

You need to clarify what mode you want to run with. Are you mixing up Open/Closed Loop with Speed Density and MAF mode, it sounds like it.

Open Loop doesn't try to go to 14.7 or what ever you have set as the Stochiometric value. It will just use the VE Table to calculate the Air Fuel Ratio. If you want to run exclusively on the VE table without the input of the O2s, you can set the AFR toi whatever you want. Now Speed Denstiy can be either Open or Closed Loop. If you want to tune the fuel trims (for stochiometric), you need to be in closed loop. The ECM will try and maintain the stochiometric value by referencing the O2 sensor voltage, which is only accurate in the 14.7 range. 13.0:1 is the PE (Power Enrichment) mode and is only accessible by reaching certain conditions (TPS% vs. RPM). In that mode it is mainly WOT that you need to address that ratio, but as Chris said your VE table needs to be very close to tune before you should attempt to tune the PE mode.

Sounds like your tuner only changed the VE table based on the WOT reading he got from a wideband, without verifying that the VE table was correct. He should have adjusted the PE multiplier, not the VE Table using a wideband. And only after the VE table has been confirmed to be correct for the Stochiometric value ... if you plan on using closed loop.

[NewVetteTuner]

After thinking about this a little more and processing my thoughts and a call from my tuner I have a few more points I would like to mention. My tuner looked at my LTFT calculated VE and his WBo2 calculated VE and a lot of the bigger differences he sees are in the lower end of the table, under no load (FTC 5 in my case most of the time) and FTC 8 and 21 sometimes.. So does the FTC modify the commanded ARF or adjust VE to compensate for the fact that is in no load mode? It seems to me like we don't want to command it to any static AFR as it needs to modify itself under no load conditions based on what the FTC's do to the calculations. Going with the average STFT and LTFT values seems to back this up. In the histogram even though I have good AVERAGE values (relative to my tuning skill), in these cells there are HUGE swings +/- (15% or so) while in the acceleration cells the values are fairly consistent.
Any thoughts on this analysis? ???

EDIT: I was cruizing the website and saw the new 1bar SD enhancement, this seems to address exactly what I am talking about?

[NewVetteTuner]

You need to clarify what mode you want to run with. Are you mixing up Open/Closed Loop with Speed Density and MAF mode, it sounds like it.

I believe we are running in SD mode (MAF off) with closed loop turned back on. The VE table was tuned in SD with a WBo2 then closed loop was turned back on per the various writup available here and elsewhere. This is one of my big issues, it makes no sence and seems to go against the premise of SD tuning itself.

[Chris@HPTuners]

the point of tuning the VE in SD mode is to match the commanded AFR to the AFR you measure on a WBO2.

If thats how you tuned it then the VE will be correct no matter what AFR you tuned it to.

[NewVetteTuner]

the point of tuning the VE in SD mode is to match the commanded AFR to the AFR you measure on a WBO2.

If thats how you tuned it then the VE will be correct no matter what AFR you tuned it to.

So if we then turn back on the stock o2's then we will have a VE table that is not tuned correctly since we are now commanding 14.7:1? That is the way I read that and also the way it seems to make sense to me.

[LS1_Sounds]

Have you read this write-up yet? It details the wideband and narrowband methods pretty well:


Basically, when tuning with a WB in open loop, SD mode you are setting your Open Loop Fuel Adder vs. ECT vs. MAP table for 13.0 as a margin of safety. This is just a commanded AFR of 13.0, what you have to do next is tune the VE table to get the commanded AFR to match the actual AFR as read by the WBO2. After they match, you return most of the tables back to their original settings, enable closed loop operation and the MAF sensor. You should then be able to directly tune other tables like the PE table by setting your divisor to the desired AFR. 13.0 is just used as a safer AFR than 14.7 since you will be running the car at high loads and high RPMs. As soon as you enable closed-loop again and return the OLFA table to stock, it will be commanding 14.7 AFR again unless you enter closed loop or PE.

Hope this helps clear things up.

[NewVetteTuner]

I think I finally get it. The commanded number can be whatever we want as long as we get the ratio right. We command 13:1 and get 13:1 we have the same VE number as if we command 14.7:1 and get 14.7:1. This flies in the face of the data I see but it could be I am just off on my setup by the amount I am seeing different from my VE vs my tuners. I just had to realize its a ratio not a hard number!

[Chris@HPTuners]

I think I finally get it. The commanded number can be whatever we want as long as we get the ratio right. We command 13:1 and get 13:1 we have the same VE number as if we command 14.7:1 and get 14.7:1. This flies in the face of the data I see but it could be I am just off on my setup by the amount I am seeing different from my VE vs my tuners. I just had to realize its a ratio not a hard number!

exactly, the airflow requirements of the engine don't change based on what AFR you are commanding.