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Thread: After Extensive E38 L92 Tuning, Gas mileage horrible and no power....

  1. #1
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    Default After Extensive E38 L92 Tuning, Gas mileage horrible and no power....

    Hi all,

    My truck has been on the Dyno 3 times, with the addition of several road tunes, to the tune of a couple thousand dollars... I do both to dial it in. Extensive work because I have been there at all times. (Side Note: You might think I am crazy, but I had a 2004 Mitsubishi EVO 8 tuned to 630 WHP and 550 WTQ, getting 27 MPG on the freeway at 85 MPH...but I digress.) Originally, I was tuned on MAF only, and running on MAF only in my 2007 Cadillac Escalade EXT 6.2L L92 E38 non AFM/VVT. This tuner is very qualified. This last go around, we followed the EFI suggested tuning methods -->(here). Tuning entirely ALL VE first with no MAF, and then switching over to MAF again after that and then blending back to stock settings at the crossover point of 4000 RPM's. We also Load Dyno'd with simulated 8K towing. Truck lost power says the butt dyno, pulling a 3500lbs. trailer on the freeway. ON Maf only previously was avg. 14 MPG towing. and all around MPG of 14 as well. Post tune, running 12 mpg in town and 8 mpg towing only 3500 lbs....

    Truck mods are:
    Completely stock 2007 L92 non VVT with approx. 8K miles on it running E38-ECM. Fresh Rebuild, and broken in properly
    Completely stock 2007 6L80E with approx. 8K miles on it running T43-TCM. Fresh rebuild and broken in properly
    3.73 Axles with adjustments in rom accordingly. Stock are 3.42's, needed new so decided to give it a little more bump.

    Everything Mechanically in the truck is new, I'm into it Parts to the tune of 25K... right down to the motor mounts.

    AFE Cold Air Intake
    JBA Shorty 1 5/8 headers
    Magnaflow High Flow Cats
    3.5" Full Catback with Magnaflow straight through shorty muffler with pre Axle dump
    Always run 91 pump

    Makes no sense.

    Edit: Step by step view of tuning order:
    After complete mechanical rebuild, first couple road tunes were for MAF only, since mods at the time were just CAI and Catback Exhaust
    Then Dyno tune tuning MAF and Spark Tables only, no VE tables.
    Added Shorty Headers and High Flow cats, since both needed replaced.
    Road tune for MAF only
    Then Dyno tune for VE since reading that headers seem to change VE decently based on several posts within this forum.

    Note, I did the Dyno tune for VE because I wanted to do it right, and was only running on MAF using the Airflow switch set to 100 RPM's....

    Edit: So on the dyno, the fuel tables for VE were saying the vehicle needed +15%-20% fuel in most of the RPM range...? Asked multiple mechanics if adding shorty headers would increase VE that much to demand that large of an increase (15%-20%) fuel? Most think 5% VE increase would be the max. So what measurement of VE being increased 1% demands what % increase in fuel? Meaning, if VE changes 1%, is that increase in VE of 1 require what measurement of increase in fuel? Put another way, an increase in VE measurement demands what in fuel measurement?

    Also worthy of noting, our calculated MAF Table in the tune file with V2 in its label, was within 1/2% or .5% post V3 tune file. So after we spent several hours on the VE tuning, MAF was hardly out of range.

    Any thoughts? If you need more info, just ask.

    Thanks in advance.

    Edited to include current tune, with my small adjustments for tires size, speedo, AC on and off with RPM, etc. Ignore the name, for it only relates to how I keep track of revisions, since we have some 45 for this truck. Map with V3 in the title is the latest fresh off of the Dyno 4.23.2021. Also include the last revision with V2 in title which is pre 3rd dyno which made 338 WHP and 387 WHTQ from the 2nd dyno time and several road tune hours. No Ve tuning in V2.
    Last edited by raceghost; May 4th, 2021 at 08:08 PM.

  2. #2
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    Put a log on the truck today. Fuel trims stay with -2% driving at various speeds and daily driving. Every now and then you see some -6~10% briefly with short terms, but long trims stay at -2%. Reset trims and received same results....

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    Will someone take a look at the "VE Coefficient Tables?" B8001, B8002, and B8003? Tello me what you see in the MapBase column compared to stock?

    Also do a compare against both roms available in Post #1. Load both and look at Calibration differences within VE Tables against each other. I notice a lot of Add cells which isn't the cause for confusion. The cause for confusion is the cells with subtraction in them, and not small subtraction either, very large amount's of subtraction.

    This is my first time at working with speed density. In the forced induction world we used MAF and straight fuel table's and injector scaling to get trims and fuel dialed in to command exact AFR's we wanted to run.

    Mind you on the Dyno, I was watching and holding the screen showing AFR's. 14.7 increasing in throttle to 12.8 throughout the rev range. I think I am misunderstanding how GM does there speed density.

    I posted this, "Question about the Original Post, since it was a post about tuning and how to. My questions is does GM use a combination of MAF/VE at or below the airflow switch threshold set at 4K rpm's, or is it only VE below 4k and MAF only above 4k, or some variation of the two? I am trying to understand how Gm does there tuning. Insight in to how it all goes together would be great." Page 73 post 728 over in the tuning thread for MAF and VE in 1 log thread, --> (here)

    As a side note, something simple, I had someone suggest front 02's might be tanked. I replaced those in October, 6 months ago, and have roughly 4k miles on them and 2 dyno sessions.... Would I not see something in the logs as too that?
    Last edited by raceghost; April 26th, 2021 at 02:12 PM.

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    Please read all 3 above posts prior to this one.

    I think I figured something out. but it leads to a couple more questions...

    My VE tables stock for both VE IMTV Open and VE IMTV Closed are identical stock.
    My new tuned VE tables are ln general richer than stock. However, my VE IMTV Open is in general leaner in low areas and richer in high areas than that of its counter part VE IMTV Closed.

    In general is I would think that the Open loop tables would be set richer in all areas than there counterpart Closed Loop Tables?
    Or should they both remain the same?

    Edit: After reading some more up on the IMTV, I am now assuming this does not mean open loop and closed loop, rather it relates to AFM mode. My truck does not have AFM mechanically, even though the rom has the tables for it, they are disabled. There for I am assuming that is why in my rom they are set the same. I am also assuming that it looks at the open tables referencing full v8 runner mode, since in AFM I assume it closed 4 of them??? Am I on the right track?

    If so, then one possibility I have found is that since these tables are rather larger in size, my tuner could have fat fingered or accidently swapped certain areas of the tables...?

    Ive also been reading and been told, that VE tables in general are set, and don't look at comparison tables for AFR/Lambda. You tell the VE table what air flow is, and it gives you whatever fuel mass relates to that amount of air...? So while yes, your watching an AFR or Lambda gauge while tuning those tables, once they are set, they are set. So plausibly, if he just did a running sweep from idle to 4k rpm, or even on up to redline, that pull only follows certain cells with in the VE tables. So surrounding tables could be richer or leaner than actually needed for economy while cruising?

    When I was tuning that Evo on MAF with fuel tables that had axis of RPM vs Load, we had to drive in all conditions on a road tune, to make sure we covering all cells that would be hit by the ECM while cruising low load for optimal AFR's for economy. Do the VE tables kind of work the same way? I know they are RPM vs MAP-KPA....

    Also as I was looking through my tuned rom, I stumbled on something with the VE Coefficient tables, and how they are generated. I took both open and closed VE tables, and copied them over to a stock rom, and it gave me a red exclamation point next to the "generate Coefficient" buttons. So I hit it, and noticed that the coefficient tables changed. What was perplexing is that the EFI live generated coefficient tables generated by the software, do not match any where close to those within my tuned rom... So this leads me to a very interesting question: Could he have forgot to generate the coefficient table, or what explanations would lead to the coefficient tables looking different with the same data in the VE tables from rom to rom?

    Scratching my head here....

    Edit: Now this is weird. In the stock rom, I only copied over the VE Tables from the tuned revision. I saved this file as to play with it a little later, and once I saved it, both the new VE tables changed data within cells. All cells got lowered by almost 15+????????? Glitch in the software? I can post pics if needed.
    Additional comments on the Glitch in the VE Tables, it is not a percentage difference nor a straight subtract difference, some cells up to -(55+) and some additions of up to +(120) in random areas. Also, the coefficient tables get generated whether you click the button or not upon saving. What is going on, I need to edit a few areas of the VE and it is not accepting my numbers, or changing them completely upon save.
    As a test, i followed through and allowed it to create the coefficient tables. Then, I copied those coefficient tables over to stock rom, and then went into the VE tables to click the button to generate VE from those coefficient settings, and it does not recreate the ve tables correctly either. I did this as a reverse operation test to se what is controlling what.
    So if I copy the tune coefficient tables read from the dyno tune file only, and paste those into a stock rom, it does regenerate the ve tables correctly, until I save, or close those windows, and then throws it all out the window and decides what it wants to enter into both the ve tables and changes what was just copied to the coefficient tables as well.
    Last edited by raceghost; April 27th, 2021 at 05:42 PM.

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    I don't understand what this is all about.

    Okay, from what I can see... you spent $25,000 on parts and $2,000 on a tuner (who you say is very qualified, but has tuned your engine to give you horrible gas mileage and no power). Are you expecting somebody here to do something for you for free, which your qualified tuner hasn't been able to do for $2,000?

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    Quote Originally Posted by statesman View Post
    I don't understand what this is all about.

    Okay, from what I can see... you spent $25,000 on parts and $2,000 on a tuner (who you say is very qualified, but has tuned your engine to give you horrible gas mileage and no power). Are you expecting somebody here to do something for you for free, which your qualified tuner hasn't been able to do for $2,000?
    Did you not read all 4 posts? I am trying to understand how GM does several things within there tuning, and how it all goes together. Your post here, is pointless, you would have been better just to scroll past.
    And second, it is responses like yours, that keep members who are trying to learn from asking questions.
    Last edited by raceghost; April 27th, 2021 at 07:29 AM.

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    Some comments:

    Shorty headers would increase airflow (cylinder airmass) by less than 5% (they are not much better than factory headers.

    Above 4000 rpm: MAF only.
    Below 4000 rpm: MAF for steady state, VE during transients.

    For SD (i.e. VE only): make sure MAF DTC shows up immedately.

    Did tuner disable trims (including possible OL ST trims) while tuning? What about AFM and VVT? Did tune only from MAF and then only from VE, and not bot at same time. Did he look at spark advance (MAF DTC causes LO table to be used)?

    IMTV is not related to AFM. Your engine has fixed intake manifold, (i.e. intake port length is fixed, no IMTV).

  8. #8
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    Gen IV factory stock tunes are usually pretty good.

    Are HO2S11/HO2S21 voltages switched several times per seconds or faster?

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    Find the correct VVE table. Pick a region and increase by 5%, calculate coeffs, do cal-only flash, test drive with failed MAF (DTC), should observe LTFT's pulling fuel approx 5%, if not need to find why.

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    Shorty headers would increase airflow (cylinder airmass) by less than 5% (they are not much better than factory headers.
    I concur, mechanics concur. Thank you. It was spend 600 for stock manifolds, or 600 for shortys with a possible gain in power, I was hopeful.

    Above 4000 rpm: MAF only.
    Below 4000 rpm: MAF for steady state, VE during transients.
    That's kind of what I was thinking, but needed clarification. Thank you.

    Edited for question: I notice in the Rom, I can set the steady state RPM... Table B8043, which is set stock to 2500 RPM. What would be the effects of setting this upwards into the 3k~3500 range? While towing, I am usually in 5th running around 2800 RPM's... I was thinking of setting this table to at least 3K rpms minimum? Thoughts on this?

    Or as I have been reading, some people are changing the crossover table from 4k down to about 2k... or some variation.

    For SD (i.e. VE only): make sure MAF DTC shows up immedately.
    Yes. Verified, because I asked about the CEL
    This was what I saw him doing as I was standing there, and holding the AFR gauge, WideBand was put in the back of Magnaflow Highflow cat, if you look in one, it looks like the honeycomb in a maf, but bigger, less dense than any other cat ive gutted, replaced, looked out, and ive seen my share. Side note, actually impressed with these little buggers...
    Side note: I disagreed with this, however, he wanted to watch the front 02's as well. I will also address a personal comment towards tuner in a moment... Please continue to read.

    Did tuner disable trims (including possible OL ST trims) while tuning? What about AFM and VVT?
    I am not sure on this relative to my previous comment. My 6.2 L92 is a 2nd Gen L92, no AFM or VVT.

    Did tune only from MAF and then only from VE, and not bot at same time.
    Yes, he did VE first, and I watched the logs, and it was commanding 20% in areas was the max I saw, and 5-10% in others... Then we switched to MAF to finish.

    Did he look at spark advance (MAF DTC causes LO table to be used)?
    Yes

    Gen IV factory stock tunes are usually pretty good.
    With MAF Tuning and Spark Tuning only, First Dyno session, we picked up roughly 20Hp and 20Tq from stock pull in the top end, 338 WHP and 387 WHTQ. So I would tend to agree with you, stock for stock, considering at that time I only had CAI and Catback Exhaust. However, we were seeing some weird fueling and things that suggested we should tune it anyway being fresh rebuild, and yes, it had 3k miles on it when I decided to dyno it the first time. Also, inside information, ALL of the 2006~2008 GM vehicles were rushed to market for the financial troubles GM was in, that ultimately led to us bailing them out in late 2008. Corners were cut in all areas for GM to get vehicles out and sold to try and not go under. So, we have seen this in several of the truck platforms with the 6.2 and 5.3's, as well as many of the 6L80E's from that era.

    Are HO2S11/HO2S21 voltages switched several times per seconds or faster?
    Can not find any of these in my rom.... Enlighten me please.

    Find the correct VVE table. Pick a region and increase by 5%, calculate coeffs, do cal-only flash, test drive with failed MAF (DTC), should observe LTFT's pulling fuel approx 5%, if not need to find why.
    I don't understand this one...? Help here also please.

    Also, I posted this in post four if you didnt see it, but since we are talking about changing the VVE Tables, check this out:
    Edit: Now this is weird. In the stock rom, I only copied over the VE Tables from the tuned revision. I saved this file as to play with it a little later, and once I saved it, both the new VE tables changed data within cells. All cells got lowered by almost 15+????????? Glitch in the software? I can post pics if needed.
    Additional comments on the Glitch in the VE Tables, it is not a percentage difference nor a straight subtract difference, some cells up to -(55+) and some additions of up to +(120) in random areas. Also, the coefficient tables get generated whether you click the button or not upon saving. What is going on, I need to edit a few areas of the VE and it is not accepting my numbers, or changing them completely upon save.
    As a test, i followed through and allowed it to create the coefficient tables. Then, I copied those coefficient tables over to stock rom, and then went into the VE tables to click the button to generate VE from those coefficient settings, and it does not recreate the ve tables correctly either. I did this as a reverse operation test to se what is controlling what.
    So if I copy the tune coefficient tables read from the dyno tune file only, and paste those into a stock rom, it does regenerate the ve tables correctly, until I save, or close those windows, and then throws it all out the window and decides what it wants to enter into both the ve tables and changes what was just copied to the coefficient tables as well.
    Software bug????

    As to my tuner, becuase I commented that he is competent, let me clarify and divulge:
    The good:
    He has several U.S. Dyno and Track records in the Dodge world, in several states. Yes, I get dodge is dodge and not GM. Speed density is the key. I didnt tune Speed density in my experience, we always did MAF based, load based/Fuel Table based tuning in the forced induction world, so speed density is new to me.
    This guy allows me to bounce things off of him he doesnt know in Import tuning, as well as is willing to teach me things I do not know about the domestics.
    I choose not to talk bad about people as a personal preference.
    I did disagree with the location of the wideband, but my cats are literally 2 inches long, and 3 inches around... Not much filtering there, but am aware, that the actual AFr's are going to be richer. I held the AFR gauge and watched the numbers from 14.7 though 12.8. So that's post cat, and small cats at that, so the actual tune is running rich, which we can see in fuel mileage. Hence why I am trying to adjust the VE tables accordingly. I will have Dual Widebands Bosch 4.9's installed next weekend, pre cat.
    I do understand GM is a different animal and that they did weird things with Virtual VE Tables, hence why I am asking questions.
    It is the Butt Dyno that is saying it makes less power. We didn't do power pulls on this last session, because I wasn't interested in a power number or a graph, I was trying to tune the areas that this truck will be seeing most of it's duty. Previous Dyno times were spent 3500 and above to 6K RPMS. This session was spent from Idle to 4K, because when I am pulling a trailer at highway speeds and it commands 4th, I see 4k rpms under tow....
    I digress.

    Thanks to anyone and everyone willing to give me info.

    Edit for share of this link: This link discusses steady state fueling, dyno vs real world, etc. This is why I dyno tune and road tune my vehicles.
    https://www.hpacademy.com/previous-w...ng-dyno-modes/
    Last edited by raceghost; April 30th, 2021 at 07:53 AM.

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