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Thread: Open Loop VE Tuning Anomaly

  1. #1

    Open Loop VE Tuning Anomaly

    I've been tuning in pure OL for quite a while now and I have gotten pretty comfortable with everything. I have the car running really good... but the pursuit of improvement continues.

    One thing that drives me crazy is a anomaly in both my VE tables. My VE tables are inconsistent from 1,200 rpm - 2,400 rpms. VE table RPM break points 1,200, 1600 and 2,400 look as they should, while 1,400 and 2000 want lower values than the rpm breaks before them. In a nutshell.... the car fuels very well and AFR Err is typically <2%.

    However, from a visual standpoint... my tables and have noticeable peaks and valleys in them from 1,200 - 2,400.

    Part of me says... if it fuels right stop worrying about it.... but there has to be a reason for the variances.

    I noticed that Fuel Trim Boundaries (under Oxygen Sensors) has the RPM boundaries set for 1,200, 1,600 and 2,400...... Now imagine that. However this section appears to be for Closed loop tuning.

    I know GM uses Fuel Trim Boundaries to basically quadrant off the VE tables into 16 areas. We have (3) rpm breakpoints and (5) VE breakpoints.

    Just to see.... I zeroed everything out for both VE and RPM in the Fuel Trim Boundaries, but it still seems that the tune wants lower VE values at 1,400 and 2,000.

    Another kicker that is that VE responds appropriately (idle is perfect) below 1,200 rpms and above say 2,600 rpms. My VE peaks around 5,100 rpms and tapers off to 6,500 rpms.

  2. #2
    Tuner in Training
    Join Date
    Dec 2016
    Posts
    46
    I went away from OL tuning preferring to use the NN approach instead but I did have my jeep running well OL . from memory you can rescale the axis so as to have more detail in the area in question , normally that's all NN territory and it dosent use VE tables at all , just the PE table

  3. #3
    Advanced Tuner
    Join Date
    Feb 2016
    Posts
    272
    Most probably the cam is causing that...don't you have 222/230 or something??

  4. #4
    with some cammed cars you will get a not so predictable looking fuel table. Give the car what it wants. Its right there in front of you. You might not have a "smoothed" to death looking fuel table. If fueling is correct , then it is correct.

  5. #5
    Quote Originally Posted by Hemituna View Post
    Most probably the cam is causing that...don't you have 222/230 or something??
    Yes, 222/230 112.5

    I disabled VE learning and it seems to have helped some.

    No matter, the AFR Err is typically <2% for the VE tables and is often <1% in most places.

    Decel has been one of the hardest components, especially when MAP wants to get around 20 KPA.

  6. #6
    Quote Originally Posted by h2.4 View Post
    with some cammed cars you will get a not so predictable looking fuel table. Give the car what it wants. Its right there in front of you. You might not have a "smoothed" to death looking fuel table. If fueling is correct , then it is correct.
    Thanks. I'm coming to terms with this. The car runs great... who cares what the table looks like.

    I've always tried not to "hack" tune it..... crazy PE, etc.... but the VE is what it is.

  7. #7
    Advanced Tuner
    Join Date
    Feb 2016
    Posts
    272
    Don't drive yourself crazy chasing perfect fuel trim numbers especially on cammed engines.
    With plenty of overlap, the 02 sensor is often getting false info anyways so is least accurate low in the rpms.
    Use it as a tuning tool, but always give the engine what it wants/likes.

    Quote Originally Posted by kenandjenn4551 View Post
    Yes, 222/230 112.5

    I disabled VE learning and it seems to have helped some.

    No matter, the AFR Err is typically <2% for the VE tables and is often <1% in most places.

    Decel has been one of the hardest components, especially when MAP wants to get around 20 KPA.

  8. #8
    Quote Originally Posted by kenandjenn4551 View Post
    Thanks. I'm coming to terms with this. The car runs great... who cares what the table looks like.

    I've always tried not to "hack" tune it..... crazy PE, etc.... but the VE is what it is.
    On some cammed cars, I've logged and dialed in the fuel table, and ended up with slight "waves" in the fuel table going up through rpm in low load areas. Then if you try to smooth those out, you get lean and rich waves in the next scanner session. The important thing that you are watching is the fueling feedback. Happy ecm, happy driveability. I almost never use smoothing option. I will manually extrapolate. It seems sometimes people spend more time at home "making" a good "looking" fuel table, rather spending that time on the dyno, or logging.

  9. #9
    It's almost like keeping the girlfriend or wife happy, everybodys girl is different and reacts different to certain things. In the end what makes her happy makes the week good, regardless of what you think, haha. Rather than what you think or somebody told you, or what you read in a book. That stuff can be good guidance, but you have to figure out the rest. The truth is in front of you, be it on the dyno, or in the logs.
    Last edited by h2.4; 2 Days Ago at 02:18 AM.

  10. #10
    Quote Originally Posted by h2.4 View Post
    It's almost like keeping the girlfriend or wife happy, everybodys girl is different and reacts different to certain things. In the end what makes her happy makes the week good, regardless of what you think, haha. Rather than what you think or somebody told you, or what you read in a book. That stuff can be good guidance, but you have to figure out the rest. The truth is in front of you, be it on the dyno, or in the logs.
    Haha I love this advice. I'm a newbie and just starting to tune VVE. It feels like summer of freshmen year in highschool all over again. Am I doing this right? Hahahaha