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Thread: Fuel Trim Basics

  1. #21
    Quote Originally Posted by 123pugsy View Post
    OK, I made some adjustments to the VE table twice.
    On the left of the pics is just disabling everything for the logging, the middle is the first adjustment and the right is the second adjustment.

    How close do the numbers need to be?
    Do I use the average as my guideline? Or the plus or the minus?

    Thanks.
    Assuming you drove around for a good while to get those numbers the fueling looks alright ish, needs less fuel at idle more everywhere else it seems. Everytime you make a VE adjustment you should be resetting your LTFTs in the scanner so it doesn't skew the data. If you put bad data in you'll get bad data out.

    A lot of this is trial and error at first but you're on the right track.

  2. #22
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    Quote Originally Posted by 3strokeEngine View Post
    Assuming you drove around for a good while to get those numbers the fueling looks alright ish, needs less fuel at idle more everywhere else it seems. Everytime you make a VE adjustment you should be resetting your LTFTs in the scanner so it doesn't skew the data. If you put bad data in you'll get bad data out.

    A lot of this is trial and error at first but you're on the right track.
    Thanks.

    Each run was 16 minutes and change, engine warmed up well.
    Tables were empty each run and repopulated as I drove.

  3. #23
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    Quote Originally Posted by 3strokeEngine View Post

    You then log LTFT in the scanner histogram with a layout that matches your VE table so you can copy you LTFT errors and paste into your VE table by right click -> paste special -> multiply by percent half.
    Damn....I read this and was trying to change all the numbers manually by 1/2%. Didn't read carefully as I was still in the flustrated learning and nervous state. Feeling better about things now.
    The paste special cut and paste works real easy.

    So, I imagine there will never come a time when LTFT's will be at zero average when scanning.
    Is it the average errors I'm supposed to copy/paste?
    When to stop this and do the next step?

    What is the next step?

    Thanks.

  4. #24
    Senior Tuner cobaltssoverbooster's Avatar
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    the environment is constantly changing. given this fact, use the copy paste method until your error values being recorded are within +/- 5% of 0.
    you should be monitoring average values when performing these steps. make sure you smooth your changes using the editor table smooth functions.

    you can feed in some ignition after working the fuel tables into a desired level of error. motors close to stock typically dont need much more than the oem ignition map on standard pup gas. these motors have fast burn head chambers so ignition around 19-23* is pretty common depending on engine behavior and installed components.
    this assumes the motor in question is N/A.
    2000 Ford Mustang - Top Sportsman

  5. #25
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    Quote Originally Posted by cobaltssoverbooster View Post
    the environment is constantly changing. given this fact, use the copy paste method until your error values being recorded are within +/- 5% of 0.
    you should be monitoring average values when performing these steps. make sure you smooth your changes using the editor table smooth functions.

    you can feed in some ignition after working the fuel tables into a desired level of error. motors close to stock typically dont need much more than the oem ignition map on standard pup gas. these motors have fast burn head chambers so ignition around 19-23* is pretty common depending on engine behavior and installed components.
    this assumes the motor in question is N/A.
    Thanks.

    I'll tweak it a bit more and call it good.
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  6. #26
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    Quote Originally Posted by 3strokeEngine View Post
    Everytime you make a VE adjustment you should be resetting your LTFTs in the scanner so it doesn't skew the data.
    How does one reset the LTFTs?

  7. #27
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    Quote Originally Posted by carzan View Post
    How does one reset the LTFTs?
    They don't actually reset. They are constantly running to give fueling info.

    To clear them from your scanner, just click Log File > Close Log File > Start Scanning
    I usually close the scanner and restart it.

  8. #28
    Quote Originally Posted by 123pugsy View Post
    They don't actually reset. They are constantly running to give fueling info.

    To clear them from your scanner, just click Log File > Close Log File > Start Scanning
    I usually close the scanner and restart it.
    The LTFTs DO reset and you MUST reset them everytime you flash a change to your VE table or it will skew your data and youll be chasing your tail. The goal here is to try to get your fuel trims +/- 2%

    Open your scanner and start scanning and look for the little green power button on the top of the scanner. Click that and it brings you into the scanner bidirectional controls.

    Navigate to engine -> fuel then click "LTFT Reset".


    On a side note LTFT works for doing these adjustments but it takes a long time for your LTFTs to average out once you reset them. I prefer logging LTFT + STFT as it seems to populate with accurate data much quicker than waiting on the LTFTs. Of course a wide band O2 is the best way to go about doing this but you can get danm close with narrowbands if you can spot trends and adjust accordingly

  9. #29
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    Quote Originally Posted by 3strokeEngine View Post
    The LTFTs DO reset and you MUST reset them everytime you flash a change to your VE table or it will skew your data and youll be chasing your tail. The goal here is to try to get your fuel trims +/- 2%

    Open your scanner and start scanning and look for the little green power button on the top of the scanner. Click that and it brings you into the scanner bidirectional controls.

    Navigate to engine -> fuel then click "LTFT Reset".


    On a side note LTFT works for doing these adjustments but it takes a long time for your LTFTs to average out once you reset them. I prefer logging LTFT + STFT as it seems to populate with accurate data much quicker than waiting on the LTFTs. Of course a wide band O2 is the best way to go about doing this but you can get danm close with narrowbands if you can spot trends and adjust accordingly


    Thanks, I hate to throw out bad info.
    It just appeared to give me a fresh blank chart that started to populate when I restarted the scanner.

    I'll have to check out the reset later.

  10. #30
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    Quote Originally Posted by 123pugsy View Post
    Thanks, I hate to throw out bad info.
    It just appeared to give me a fresh blank chart that started to populate when I restarted the scanner.

    I'll have to check out the reset later.
    It doesnt reset your charts fuel trim it resets the LTFTs in the pcm that it learned over time
    1997 30th SS. Torqhead 24x, TFS heads, 223/235 cam, 4l80e, S60 D1SC 14psi

  11. #31
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    Quote Originally Posted by anniversaryss View Post
    It doesnt reset your charts fuel trim it resets the LTFTs in the pcm that it learned over time
    Thanks.

  12. #32
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    OK.

    Changes made and trims reset (properly this time) before logging.

    I think it looks good, but I'm no expert as you all know.
    Tell me what you all think, please.
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  13. #33
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    No comments? What's next?
    Will these numbers change after turning the MAF back on?

  14. #34
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    Quote Originally Posted by 123pugsy View Post
    No comments? What's next?
    Will these numbers change after turning the MAF back on?
    I answered my own question.
    Reset the MAF and proceeded to log huge LTFT's.
    Apparently, my intake hose is leaking. The numbers told me to search for the problem.

  15. #35
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    I wasn't happy with the leaking intake tube, so I made up a solid aluminum tube with zero leaks and same results with MAF reinstated.
    High L & STFT's and no intake leak.
    Should I be looking at a bad MAF sensor or do I now need to do some different tuning for the MAF?
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  16. #36
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    I'm running a similar setup in a 99 camaro with T56. 5.3 with flat tops, 243 heads, ls1 intake and injectors. LS2 cam from a corvette. Started with the 99 camaro ECM stock program and have tuned VE and MAF to 0 to -5 LTFT in most cells, runs really well. If you think my VE or MAF info will help let me know.

  17. #37
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    Quote Originally Posted by KDS View Post
    I'm running a similar setup in a 99 camaro with T56. 5.3 with flat tops, 243 heads, ls1 intake and injectors. LS2 cam from a corvette. Started with the 99 camaro ECM stock program and have tuned VE and MAF to 0 to -5 LTFT in most cells, runs really well. If you think my VE or MAF info will help let me know.
    Thanks.

    I wouldn't mind seeing the tune.

  18. #38
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    good stuff here - trying to get my trims in check as well

  19. #39
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    Quote Originally Posted by K Rob View Post
    good stuff here - trying to get my trims in check as well

    How you enjoying the learning curve?

    Be careful with spark advance if you change the tune. I developed piston slap after going a bit too extreme.
    Or perhaps the 5.3 gets piston slap commonly? Don't know.

  20. #40
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    Quote Originally Posted by 123pugsy View Post
    How you enjoying the learning curve? .
    Quote Originally Posted by 123pugsy View Post
    Should I be looking at a bad MAF sensor
    what did you come up with with the high lt/fts after maf hooked up?