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VE tables and LTFT histograms?

This is a discussion on VE tables and LTFT histograms? within the Computer & Tuning forums, part of the LSx Technical Help Section category; Using HPtuner. Making logs with LTFT histograms and it's running lean. I can only fill the lower portion of the ...

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    Moderator Firebirdjones's Avatar
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    VE tables and LTFT histograms?

    Using HPtuner. Making logs with LTFT histograms and it's running lean. I can only fill the lower portion of the histogram due to staying out of PE mode. I need to transfer this histogram to the VE table to richen the car by % mulitply,,,but with only the lower portion of the histogram filled, what do you do about the higher portion of the VE table? Say 3,500 rpms and above? Should I not worry about it? Larry.

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    Mrs.'s Boobies
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    Without a wideband to measure your PE fueling, I would filter it out (ignore it). But you will be able to see the trend of the VE table after you make the LTFT adjustments. Since you are running lean, I would adjust the VE table up based on the fuel trim trends. This should get you close, but you will need to monitor the fuel with a wideband either on a dyno or throught HPT.
    George P. Lara
    Mine 2001 Camaro SS #0391: FQuick Garage
    Mrs.'s 2002 Camaro SS #7072: FQuick Garage

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    Moderator Firebirdjones's Avatar
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    Thanks man,,,I think I have a grasp on the VE tables now. I made a datalog run with the MAF disabled and found alot of +4 and +5 on the LTFT histogram with easy to moderate throttle to stay out of PE,,,,,so I made the appropriate changes in the VE table and made another run,,,so on and so forth,,,On the last datalog my LTFT histogram was mostly 0's with a few -1's and only a couple of -2's and I was pretty happy with that so I left it as is and burned that into the car,,,and reenabled the MAF sensor.

    I went for another datalog run with the MAF working now,,,and looking at the LTFT histogram with light to moderate throttle,,,it's now +12 and +14 most everywhere. What is up with that?
    Do I need to adjust the MAF table now or something? It acts like it wants tons more fuel after I just got done adding fuel in the VE tables.
    I guess I need add to the MAF table now (12-14%) to correct this? Larry.

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    Senior Member mrr23's Avatar
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    dark bowling green
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    i've been playing with VE tuning now. been reading up on your posts on hptuners board as well. made my first adjustments today. will see how it does tomorrow on the drive to work.

    just trying to get the hang of it before i put the 408 in.

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    Moderator Firebirdjones's Avatar
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    Thats cool. I finally got a handle on the VE tables. I find that rather easy. I am still playing with the MAF table though. I found out I was datalogging for the MAF incorrectly. I needed to change my LTFT datalog to read HZ so I can match it with the MAF table. Now that I know,,,I am going to give it a try this morning and see if I can get the MAF tables in line, they are all out of wack at the moment.
    I found that once I got my VE table where it should be, it kinda threw off the MAF LTFT's. I'm still learning but slowly getting the hang of it. Larry.

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    Mrs.'s Boobies
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    You can tune the MAF table either by LTFT%, AFR Error % or log Dynamic Cylinder in g/sec. With the LTFT% and AFR Error % all you need to do is Paste Special %. If logging Dynamic Cylider Air (g/sec), you can directly paste those numbers to the MAF Transfer Table (MAF Frequency). I have made up a simple Dynamic Air --> MAF Hz excel sheet to allow me to use the Paste Special % and correct the MAF Table, it comes out dead nuts on.

    Oh, and yes ... once the VE table is "spot on", when re-enabling the MAF, you will find it needs adjustment.

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    Moderator Firebirdjones's Avatar
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    Yep got it working. I set up a histogram for MAF with % and did some datalogging. At first in the morning it was about 60 degrees but it still wanted fuel. I had the LTFT at about -1 and -2 everywhere and I was happy. Later today the temp has risen to about 78-80 degrees and I had to run an errand. I hooked up the laptop just to datalog for the heck of it. Sheeeesh the temp change put everything on the rich side. My LTFT's were -8 to -10 in most places. So I checked the MAF tables/histogram and pulled a little bit of fuel out. I can't believe the LTFT's would swing that much for such a small ambient temperature change,,,,what a pain.
    I have been told to keep the LTFT's in the negative at all times so it is never added to PE when you go full throttle. In order to keep them all negative on a cool day would mean the car is running too rich when it warms up outside. Guess I have to find a happy medium and live with it. Larry.

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    Senior Member mrr23's Avatar
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    yep, i've had many a disussion with so called tuners over temperture being a variable factor. my reasoning for having a handheld vs a dynotune from a local shop is so you can make changes whenever you wanted for changing conditions. their reason was do a dyno tune and the sensors will make up the difference. hardly. weather makes a huge difference in tuning. and sensors can only correct to the limits of the tables they are run off of.

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    Mrs.'s Boobies
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    You guys need to realize that the LONG TERM fuel trims will take a while to stabilize. It is not uncommon to see wide fluctuations in the LTFTs, even on stock unmodified cars directly from the factory. This is the computer working the fuel rich, then lean and back and forth trying to see where it should be. It references the last saved settings and calculates the new proposed fuel trimming. If you really want to see what your LTFT really are, you need to drive the car for at least 30 minutes or 50 miles, so the LTFT will settle. If you want to see the unbaised (from historical data) fuel corrections, log the SHORT TERM fuel trims. It is imperative to make changes to the VE and MAF fuel tables during on climate session, otherwise you will be chasing your tail. My fuel trims are always the same ... wether it is 40 degrees outside in the dark early morning commute before traffic, or 100 degree afternoon in rush horu traffic. Heck, even when I am along the coast (50 degrees, 30.10 baro, 60% humidity) then I drive up to the high desert (110 degrees, 26.50 baro, 10% humidity) and my LTFTs are within -1% to -5%. I street tuned my 1500HD and my 2001 Camaro SS to run the MAF in Closed Loop BTW (started with an SDOL tune). You need to allow the ECM to do it's job. Saying the sensor have limits only mean the tuner messed something up. You need a good tuner who fully understands what they are doing and can calibrate the fuel maps properly. Then you will see what I am talking about. Otherwise, just stick a carb on it and be done ... essentially that is what you are doing (but at a higher cost).

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    Moderator Firebirdjones's Avatar
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    LOL, I can't leave my carbed cars alone either,,,everytime I take the chevelle to the track, (or the firebird for that matter) I am into the carb and changing jets, the weather plays a huge roll in fueling.

    This camaro on the other hand, I expected the computer to keep it in check and not swing so much. I am positive my LTFT's have been settled in with every adjustment I was making. I was told to also watch the STFT's and when they slow down their swing, plus or minus 3% then it's a good bet the LTFT's have settled. If the STFT's are swinging higher then more driving is needed. Even so,,,I drove for quite a while each time,,,as it takes alot of time, throttle position, and various speeds and loads to fill that stinking histogram,,,lol. But I think what I plan to do is wait until the weather gets to about 85 degrees around here with the typical Cinci humidity and play with the tune some more. Thats a happy medium temp, so if I can get the LTFT's around -3 or -4 to compensate for the cooler fall weather, then I will leave it at that. I did notice something good out of all this today,,,since the car was running so lean it always had about 2 degrees of knock retard (still run stock timing tables) but since I have had to add fuel to get the LTFT's close to where they should be,,,I did a couple of full throttle logs today and the knock retard is completely gone now, the extra fuel helped to quench it.
    I'm not a novice tuner per say,,,have plenty of experience with carbs and distributors,,,it's this computer that is killing me.
    Anyway,,,I do have another question if you care to be entertained. I set up a histogram with MAF hz readings in linear fashion to match up with the MAF table. I noticed filling that MAF histogram is primarily related to your throttle position which makes sense, (more throttle more air) but how far can I take the throttle and use this table for adjustment? Can I go full throttle and do some upper rpm fueling or does the PE mode mess that up too? Hope that question makes sense. Larry.

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    Mrs.'s Boobies
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    I am always willing to be entertained. I started tuning with Q-Jets, I know I'm an odd ball.

    Anyway, when tuning the MAF via LTFT be cautious to harsh throttle transitions. The ECM uses the MAF for steady state fueling, but the VE table for abrupt throttle transitions. Then anything after 4000 under WOT is all MAF. Without a wideband, I would not go into PE mode, as the fuel trims will stop updating and provide no info if the fuel is too rich. It will add fuel if you were lean, like before. And yes, extra fuel will quench knock.

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    Senior Member mrr23's Avatar
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    i appreciate you taking time out to explain this to us. helps out a lot. i'm still doing the VE table, right now. i'm just getting ahead for when it comes time for the MAF tuning.

    i've been using the STFT to make corrections with. i did 5 logs yesterday and review them all before making my first change to the VE table. looking over todays log to see how it did.
    Last edited by mrr23; 04-03-2007 at 04:48 PM.

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    Senior Member mrr23's Avatar
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    looking at the STFT and LTFT histograms. all are at 0% that got logged.

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    Okay so I'm a moron... =) Not really just learning the ropes... the VE tables are for everyday normal driving and then it swaps over to the PE tables (whichever one it deems if you have two) for the WOT trips?? I'm just trying to get a grasp and trying to read as much to understand in a quick manner so that I can tune my car successfully... Thanks for "entertaining" the retarded question...

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    Moderator Firebirdjones's Avatar
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    Hey Mrr23,,,are you logging your LTFT's for your VE table with the MAF disabled? I seemed to have forgotten this minor detail when I started and had to do it all over again,,,lol.

    Thanks 12 second SS,,,I am going to log some more LTFT's with the MAF and try to be smoother on the throttle and see how it looks. I will do my best to stay out of PE and under 4,000 rpms and fill as much of the histograms as I can.
    I may go back to my original MAF table and start over because of how I started.
    Looking at my LTFT histogram with the MAF working, everything was +10 and +12 in the lower sections so I just took the MAF table and raised the entire table 8% accross the board. This got everything close on the LTFT histogram. At this point I figured out how to plot the MAF histogram and started using that,,,still some of it was +2 or +3 but alot of the MAF histo was 0 or -1,,I left those alone and concentrated on the + areas. It took 2-3 tries before I thought I had it licked. Not sure if I went about this the right way or if I should start over, since I added 8% right off the bat which added fuel above 4,000 rpms for full throttle etc...and it may be too fat in that area now. Need a wideband as you suggested to be sure.
    I really can't tell any performance difference on the street with these changes. At first I thought maybe the throttle response was better, but hard to tell. I do know the LTFT's are still better than they were when stock,,,even though I am a novice at this.
    When it was stock and I had the gauge screen on the lap top driving around the left bank LTFT graph/bar would just turn red and stop moving,,,lol. I knew something was out of whack.
    Should I start over with what I have done above so far or should I keep pecking away at it? Larry.

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    Moderator Firebirdjones's Avatar
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    Heres a more in depth question for ya. When filling the MAF histogram to use for the MAF table,,,(I have mine set up for % + or -) to tell me how much to change the MAF table. What do I want to shoot for on the MAF histogram? All 0's? or should I try to keep this a little on the rich side with -1 or -2 much like the LTFT's? Your thoughts on this? Larry.

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    Mrs.'s Boobies
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    Quote Originally Posted by mrr23 View Post
    i appreciate you taking time out to explain this to us. helps out a lot. i'm still doing the VE table, right now. i'm just getting ahead for when it comes time for the MAF tuning.

    i've been using the STFT to make corrections with. i did 5 logs yesterday and review them all before making my first change to the VE table. looking over todays log to see how it did.

    looking at the STFT and LTFT histograms. all are at 0% that got logged.
    Just trying to lend a helping hand, and ensure people understand what the tables do and what they are for. Seems you are doing a good job!

    Quote Originally Posted by 98turbols1 View Post
    Okay so I'm a moron... =) Not really just learning the ropes... the VE tables are for everyday normal driving and then it swaps over to the PE tables (whichever one it deems if you have two) for the WOT trips?? I'm just trying to get a grasp and trying to read as much to understand in a quick manner so that I can tune my car successfully... Thanks for "entertaining" the retarded question...
    The VE table is used for harsh throttle transitions (like when autocrossing), the MAF is used during soft throttle transitions (like when gramma is driving) or steady state cruising, as well as WOT above 4000 rpms. PE = Power Enrichment is a commanded (richer) fuel AFR when certain parameters are met. While driving around below those threasholds, the ECM will maitain stoich AFR (defined by the stoich value = 14.62857). But when you mash the throttle, the PE Table kicks in and commands 12.8 (where I set it at, stock is 13.0 to 11.70). The values in the PE Table are based on dividing the stoich AFR by the new commanded AFR (14.62/12.80 = 1.143). The ECM will always go to the richer table between the OLFA, PE, or COT enrichment tables.

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    Mrs.'s Boobies
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    Quote Originally Posted by Firebirdjones View Post
    Hey Mrr23,,,are you logging your LTFT's for your VE table with the MAF disabled? I seemed to have forgotten this minor detail when I started and had to do it all over again,,,lol.

    Thanks 12 second SS,,,I am going to log some more LTFT's with the MAF and try to be smoother on the throttle and see how it looks. I will do my best to stay out of PE and under 4,000 rpms and fill as much of the histograms as I can.
    I may go back to my original MAF table and start over because of how I started.
    Looking at my LTFT histogram with the MAF working, everything was +10 and +12 in the lower sections so I just took the MAF table and raised the entire table 8% accross the board. This got everything close on the LTFT histogram. At this point I figured out how to plot the MAF histogram and started using that,,,still some of it was +2 or +3 but alot of the MAF histo was 0 or -1,,I left those alone and concentrated on the + areas. It took 2-3 tries before I thought I had it licked. Not sure if I went about this the right way or if I should start over, since I added 8% right off the bat which added fuel above 4,000 rpms for full throttle etc...and it may be too fat in that area now. Need a wideband as you suggested to be sure.
    I really can't tell any performance difference on the street with these changes. At first I thought maybe the throttle response was better, but hard to tell. I do know the LTFT's are still better than they were when stock,,,even though I am a novice at this.
    When it was stock and I had the gauge screen on the lap top driving around the left bank LTFT graph/bar would just turn red and stop moving,,,lol. I knew something was out of whack.
    Should I start over with what I have done above so far or should I keep pecking away at it? Larry.
    That is a good pratice, if you see that the fuel is off by at least (say) 10%, then you should modify the fuel table (VE or MAF) by that amount. This will get you closer to your desired fuel ratio without unnecessarily going lean to find out you just need an extra (per our example) 10%. You did good. Now, one thing I must note that most of these tuning docs. have not touched on prior to commencing tuning. Be sure that the LTFT, or at least the O2 mV readings, are fluctuating by similar amounts. Meaning if one side is slow to respond or the values are high compared to an opposing back ... in spect the mechanical condition of the engine/vehicle to ensure a mechanical problem will not worsen your tune. Because if you have an exhaust leak and tune based on that bank (for wideband tuners) or your fueltrim are skewed too lean or rich, then all you may accomplish is tuning the car more out of whack. Please be cautious when tuning.

    Quote Originally Posted by Firebirdjones View Post
    Heres a more in depth question for ya. When filling the MAF histogram to use for the MAF table,,,(I have mine set up for % + or -) to tell me how much to change the MAF table. What do I want to shoot for on the MAF histogram? All 0's? or should I try to keep this a little on the rich side with -1 or -2 much like the LTFT's? Your thoughts on this? Larry.
    I have mine set for 2 decimal places for higher resolution, but I use a wideband. Sure, you can try and shoot for all 0s, but realistically, I would be contant with staying around -4% to 0%. Also, be sure you are using the A = average, versus the max/min/last values, for all your corrections.

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    Moderator Firebirdjones's Avatar
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    Good info to know. Thanks for pointing that out. Yes I am using "A" for average on my datalogs and stuff, and my 02 sensors seem to be very active.
    I will keep tinkering, it's good practice, eventually I will hit on something.
    I wanted to do some datalogging today but the temps went from 82 yesterday to 40 today So I am going to wait for some warmer days.
    Hey while I am at it,,,are you familiar with DFCO tuning? I was thinking it's not enabled on factory tunes? How do I tell?
    My car revs up nicely (in park or neutral) but the engine is slow to come back to idle. I was thinking the injector cut off had something to do with that. Am I on the right track or is DFCO not even working at this point?
    How do I fix the slow "return idle speed" thingy?

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    DFCO only works while cruising or slowing down. To find DFCO go to Engine-Fuel Control-fuel Cut Off, on the second colunm you will see DFCO Enable Temp. It should be set around 131F or so. I have played around with it quite a few times on my cars. Since it is set already and not much more to tune, I have not played with them for a while, but I do remember some things for it. Your RPMs coming back down to idle slowly would be the job of the Throttle Follower Table, under Idle-Airflow ... towards the bottom right.

    DFCO doesn't do what you are describing, if it was DFCO the engine would stall ... since no fuel nor spark would be present. Hence why it is disabled upon reaching a set MPH and dropping below that MPH.

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