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Thread: Throttle Cracker Tuning Question {B4309}

  1. #21
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    On throttle bucking:
    Frames 1338-1446, STFT goes a bit positive, LTFT are about -6.5, everything else looks fine, some bucking here but it isn’t terrible.
    Frames 2654-2697, bucking is pretty bad, lower TPS seems to cause worse bucking, STFT are a bit negative but everything else looks good.
    Frames 2844-3029, some bucking but it isn’t terrible, everything looks fine, STFT may be a bit negative.
    Frames 4409-4707, some bucking, STFT are a bit negative, everything else looks fine.
    Frames 5241-5292, bad bucking, STFT are negative, IAC steps makes a big jump in the middle of it. My TPS changed a tiny hair, might have caused the IAC change.
    Frames 7118-7202, slight bucking, have the same IAC change as above. Looks like another tiny TPS change, probably the cause of the IAC change.
    Frames 8546-8636, bad bucking, STFT start pretty negative then become less negative, everything else looks fine.
    Frames 8834-9138, some bucking, everything looks pretty good, STFT are a bit negative but not bad. STFT2 goes positive.
    Frames 9389-9748, a little choppy, everything looks pretty good.
    Frames 10190-10299, a little choppy, WO2 is a little lean, STFT are negative at first but then look pretty good. First bit of STFT negativity is opposite first bit of LTFT positivity.
    Frames 10562-10665, a little choppy, WO2 is a bit lean, everything else looks good although the rapid IAC change occurs.
    Off throttle bucking:
    Frames 1916-2036, STFT are trending positive when bucking starts, LTFT is okay, WO2 is biased lean, car is smooth then has a but of bucking starting at about 1230RPM, not terrible though.
    Frames 22371-2498, pretty much the same as above.

    Again thanks for the help! I'm wondering if I need to spend more time adjusting the VE table via CALC.VET? Below is the log:

  2. #22
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    Your fueling isn't pulling in as nicely as it should be. I ran some diagnostics on your log and found lower than expected airflow readings with low MAP values. This could indicate a possible air leak in your intake manifold. Check for air leaks and fix any leaks you find before doing your next log. A smoke test of your intake would be ideal, but if you can't manage that then just check for broken or split air hoses and run the engine at idle and listen for any hissing sounds.

    Log the same PIDs as usual... and make sure you log ALL of them.
    Attached Files Attached Files

  3. #23
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    I checked for vacuum leaks Wednesday night. I couldn't hear anything, I wiggled all hoses and couldn't get the engine to change speed or make weird noises. I sprayed every spot with a seal or hose with carb cleaner and didn't experience any changes. The engine has a fair number of miles on it, but I couldn't find any potential vacuum leaks.

    I did get another log. Don't worry, I saved all your required PIDs to Statesman.pid the last time I logged!

    ECT hits 80C around frame 1800. Below are some notes. Overall nothing has gotten worse, I did notice more improvement with low TPS and low RPM bucking still being reduced a bit.

    Steady throttle pull:
    Frames 2083-2152
    Frames 3519-3590

    Low TPS bucking:
    Frames 2359-2449
    Frames 2866-2922
    Frames 4749-4811
    Frames 5020-5085

    Steady throttle cruise:
    Frames 2603-2853
    Frames 3196-3412
    Frames 4084-4403
    Frames 10992-11095
    Frames 12187-12302

    Off throttle deceleration with bucking:
    Frames 3006-3181
    Frames 4412-4438
    Frames 9973-10015

    Here is the log file:

    GTO Jan 10 2019 IBC to dinner.efi

  4. #24
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    Quote Originally Posted by pinstripebob View Post
    I checked for vacuum leaks Wednesday night. I couldn't hear anything, I wiggled all hoses and couldn't get the engine to change speed or make weird noises. I sprayed every spot with a seal or hose with carb cleaner and didn't experience any changes. The engine has a fair number of miles on it, but I couldn't find any potential vacuum leaks.
    Okay. I'll have to hunt down the reason that the numbers don't look quite right.

    A few questions for you....

    Have you recently (or ever) cleaned your MAF sensor?
    Are you using an oil impregnated air filter (like a K&N)?
    Is your intake tubing stock or modified?

    We'll keep working on your bucking while I'm trying to figure out why your fueling doesn't want to straighten out.
    Last edited by statesman; May 2nd, 2019 at 12:43 AM.

  5. #25
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    Let me know what you think. I don't have a problem doing some troubleshooting.

    To answer your questions:

    1. I have cleaned it, I think the last time I cleaned it was 3 or 4 months ago. It's a stock replacement from AutoZone, maybe 3 years old.
    2. I use a Green brand filter that is oiled. I'm very careful when I oil it, and the last time I cleaned/oiled it I cleaned the MAF sensor after driving for a couple weeks.
    3. My intake tubing is modified. I've read you should have 6" before/after the MAF of straight pipe, which I don't. Below is a picture of my bay (red car) versus a stock bay (yellow car).

    I'm still wondering if my VE table needs more work, maybe that would help us out? MAF seems to be in fairly good shape. I've done a couple CALC.VET logs and the correction factor to the MAF curve is never more than 2%.

    Mine:
    Click image for larger version. 

Name:	IMG_20190114_061534.jpg 
Views:	180 
Size:	1.02 MB 
ID:	22604

    Stock:
    Click image for larger version. 

Name:	stock engine.jpg 
Views:	159 
Size:	51.2 KB 
ID:	22605

  6. #26
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    Quote Originally Posted by pinstripebob View Post
    I'm still wondering if my VE table needs more work, maybe that would help us out?
    No, we're in MAF only mode so the VE doesn't come into play. Leave the VE table until we get the fueling right.

    Alright, now I see why I got those numbers when I analyzed your log.

    Do a log with the tune file I posted... fueling will still be out, but I'm more interested in your low throttle bucking with this tune update. I do have another fuel adjusting technique which is more suitable for your intake plumbing... I'll use that next time.

  7. #27
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    Sounds good! I'll give it a go and post a log.

  8. #28
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    Got the log! Overall the car seems about the same, bucking may have been reduced a bit. I can induce bucking with low RPM off-throttle or low TPS inputs. Shifts seem a bit smoother to me. ECT hits 80C around frame 1800, below are my notes on areas with or without bucking. I did notice a few spots where voltage varied, especially toward the very end of the log.

    Steady TPS cruising, no bucking:
    Frames 3591-3733
    Frames 3931-4096
    Frames 4308-4677
    Frames 9884-10,105
    Frames 10,374-10,617

    Steady TPS acceleration:
    Frames 2659-2740

    Steady TPS cruising, some bucking:
    Frames 2877-3034
    Frames 3739-3920
    Frames 4120-4300
    Frames 8348-8387
    Frames 8920-9005
    Frames 11,987-12,231

    Off throttle deceleration, some bucking:
    Frames 3242-3485
    Frames 5218-5258
    Frames 5299-5338
    Frames 5380-5415
    Frames 5556-5631
    Frames 8562-8602
    Frames 8703-8821
    Attached Files Attached Files

  9. #29
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    Post got cut off again. Womp womp.

    Off throttle deceleration, some bucking:
    Frames 3242-3485
    Frames 5218-5258
    Frames 5299-5338
    Frames 5380-5415
    Frames 5556-5631
    Frames 8562-8602
    Frames 8703-8821 – Bucking stopped for a moment then came back
    Frames 10,116-10,231
    Frames 12,748-12,784


    Off throttle deceleration, no bucking:
    Frames 6073-6160
    Frames 7765-7863
    Frames 9491-9556
    Frames 10,627-10,730

    Some throttle then no throttle, some bucking occurred:
    Frames 13,891-13,938

    Notable drops or spikes in voltage:
    Frames 837-857 (not up to operating temp, though)
    Frames 1093-1104
    Frames 8516-8525
    Frames 14,545-14,553

    Let me know what you think. I'm on country roads, so if there is a specific driving style or scenario you want me to try just say the word. Thanks!

    Log:
    GTO Jan 16 2019 IBC to home.efi

  10. #30
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    Don't drive on my Mod4 tune file anymore.... it goes lean in PE. This update won't do anything to help your bucking, it's just to get fueling better.

    I tried using my alternate method to adjust fueling and it can't find a solution which maintains a proper MAF curve. I think your aftermarket MAF sensor is junk. How would you feel about replacing the MAF sensor?... I think even a second-hand factory sensor from a junkyard would be better than the sensor you're using now.

    I did make an adjustment for your transients... so still do a log with this update.
    Last edited by statesman; May 2nd, 2019 at 12:42 AM.

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