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Thread: negative timing on Idle

  1. #41
    For me changing those would not fix the timing issue. If the poster is willing to try my fix and post what the result is that would be great. Rather good or bad. It?s like there is something missing to edit to do it the way that makes sense. I am just happy to finally have negative timing fixed and my fuel trims are within 5 percent at idle. They run and shift perfect now. I just know that leaning the maf table increases timing. Changing virtual torque does nothing for me. Maybe since these are swapped vehicles it has something to do with it.

  2. #42
    My fuel trims are fine so I have no issues and the swap runs perfect. My negative timing was in a completely stock engine. There should be no need to adjust virtual torque. The only change would be a intake tube. If I dialed the fuel trims in off the maf to close to zero it would run -15 degrees at idle. I lean it out a slight amount and the timing and fuel trims would be happy. Applied this to a cam swap and fixed negative timing again and it runs great.

  3. #43
    Senior Tuner Higgs Boson's Avatar
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    I guess you can heal a wound with a band-aid. ;-)

    Whatever works for you, right?

  4. #44
    ok so i did what you suggested removing from my maf table and it now fluctuates attached a logpos spark.hpl

  5. #45
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    Quote Originally Posted by tlavoie87 View Post
    ok so i did what you suggested removing from my maf table and it now fluctuates attached a logpos spark.hpl
    Because that is not the right way to fix it.
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  6. #46
    I wish someone makes a Gen5 idle tuning guide. ☺

  7. #47
    Senior Tuner Higgs Boson's Avatar
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    Quote Originally Posted by ahmedabri97 View Post
    I wish someone makes a Gen5 idle tuning guide. ☺
    Tune your MAF perfectly
    Tune your VVE perfectly
    (these two alone may be enough to get idle right in a mild application, don't assume you need to get crazy with torque tables)

    Spark and Min Spark need to be not stupid, do not try to force it to idle with a certain amount of timing. Many cars and trucks idle with 5 degrees of lead, of course you don't want -15 but 15 is also not mandatory.
    Zero Pedal External Load Table needs to more like zero pedal torque, log it
    Airmass and MAP Coefficients BOTH need to be adjusted properly depending on what you have done to the car, typically only with a cam swap or the like major change.


    many people do not tune VVE, MAF is off and before taking care of that they chase torque model adjustments with no change.....fueling must be correct or spark will be wrong and fluctuate, etc.

    when in doubt, go back to stock and start over (regarding idle).

  8. #48
    Thank you very much Higgs.

  9. #49
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    Lets say we installed a cam, fueling is good, and have spark ploblems and need to adjust Virtual Torque, what is the correct way?, add/remove from -10 to 30 degree axis and 500-1000 RPM axis? Intake exhaust angle? or need to log on idle and adjust only on the spark axis i want it to idle? adjust only in the idle intake/exhaust angle positions?
    Just need to clear it on my mind. thanks

  10. #50
    Senior Tuner Higgs Boson's Avatar
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    Quote Originally Posted by castorjames View Post
    Lets say we installed a cam, fueling is good, and have spark ploblems and need to adjust Virtual Torque, what is the correct way?, add/remove from -10 to 30 degree axis and 500-1000 RPM axis? Intake exhaust angle? or need to log on idle and adjust only on the spark axis i want it to idle? adjust only in the idle intake/exhaust angle positions?
    Just need to clear it on my mind. thanks
    first tune your zero pedal external load table then airmass and map vtt if needed.

    most aftermarket cams don't really move much, many use 0 (full advance) until higher RPMs and only retard 1 or 2, so get the right data from your cam people and use that. if you are only having problems at idle then you would only need to adjust the 0 VTT tables since the cam doesn't retard at idle anyways.

  11. #51
    Quote Originally Posted by Higgs Boson View Post
    first tune your zero pedal external load table then airmass and map vtt if needed.

    most aftermarket cams don't really move much, many use 0 (full advance) until higher RPMs and only retard 1 or 2, so get the right data from your cam people and use that. if you are only having problems at idle then you would only need to adjust the 0 VTT tables since the cam doesn't retard at idle anyways.
    Higgs dumb question nut how do you tune zero pedal external load? what should i be loggng or charting

  12. #52
    Senior Tuner Higgs Boson's Avatar
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    Quote Originally Posted by tlavoie87 View Post
    Higgs dumb question nut how do you tune zero pedal external load? what should i be loggng or charting
    make an external load table in your scanner and log zero pedal torque into it

  13. #53
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    Higgs were does this zero pedal external load come into play? Is there a table in the editor for it? Or are you suggesting log it and apply to Virtual Torque?

    Currently using Version 4.3.153 Beta,and yes I see there is an update

  14. #54
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    Quote Originally Posted by Steve899 View Post
    Higgs were does this zero pedal external load come into play? Is there a table in the editor for it? Or are you suggesting log it and apply to Virtual Torque?

    Currently using Version 4.3.153 Beta,and yes I see there is an update
    Engine>Idle>Torque>External Load

  15. #55
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    Thanks sevinn

    Engine >Idle >(RPM or Airflow) >torque doesn't exist in my tune,
    I only have RPM or Airflow

    Opened another tune and yes I see it RPM or Torque
    So yes
    Engine >Idle >Torque>External Load is there
    Last edited by Steve899; 02-18-2019 at 12:57 PM.

  16. #56
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    Quote Originally Posted by Steve899 View Post
    Thanks sevinn

    Engine >Idle >(RPM or Airflow) >torque doesn't exist in my tune,
    I only have RPM or Airflow

    Opened another tune and yes I see it RPM or Torque
    So yes
    Engine >Idle >Torque>External Load is there
    What vehicle are you tuning? Sounds like you are looking at a gen4 vehicle.

  17. #57
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    Tuning a 64 Chevy II
    Its a gen v , added Cam , Headers , Intake , LT4 supercharger


    Oh my sevinn , yes you are correct !!!
    I brought up the old LS3 Gen IV tune up for this car, when I tried to follow along with this thread
    Last edited by Steve899; 02-19-2019 at 12:02 PM.

  18. #58
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    Quote Originally Posted by Steve899 View Post
    Tuning a 64 Chevy II
    Its a gen v , added Cam , Headers , Intake , LT4 supercharger


    Oh my sevinn , yes you are correct !!!
    I brought up the old LS3 Gen IV tune up for this car, when I tried to follow along with this thread
    Sounds like a pretty sweet setup! But glad we got that mystery solved lol

  19. #59
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    I wanted to bring this thread back since I tried this and it seems to have no effect.

    I think I get it and kind of understand what we are trying to do here. I logged zero pedal engine torque in the scanner into a histogram with the x and y axis the same as the external load table. I logged at cold engine oil temps too. I then took some more runs and averaged them and can see the trend in zero pedal engine torque, which is also the same trend I see in the external load table (values both increasing and decreasing from the target idle speed (around 600 rpms)) both increase or decrease. This dosen't make any sense if this "external load" table is supposed to be a baseline for how much torque the engine needs to maintain a certain idle speed. Theoretically you would think the table would start off a the lowest RPM with the lowest torque and as RPM goes up, frictional forces go up, and the torque should increase.

    Anyway it hasn't had any effect when I change it to what the PCM is outputting for zero pedal engine torque. So I figured that kind of makes sense, since the PCM only uses this table as the base or "first guess" at torque, so the PCM has already been trying to adapt and has commanded a different torque at idle, which I assume is why the PCM tries to open the throttle so much to increase airmass (torque) using the "predicted torque control" method and then uses the "immediate torque control method" to try to reduce torque since its got the throttle open so much. So then any slight positive timing adjustments the PCM tried to make to control speed throws the car forward because timing is so far reduced and the car lurches forward and everyone things your car is broke and a POS.

    I also tried doing the usual decrease the virtual torque tables in the idle rpms region and decreasing the lower spark VT tables more than the higher spark ones (to try to trick the PCM into using a higher spark value to get torque). This somewhat works in that it gets it idling at a higher, non-negative spark value, but you still get a lot of lurching forward and vibration (I expect some from a cammed engine but I know with better (smoother) spark the idle quality could be a lot better). I was hoping after decreasing the torque in the VT tables at idle and then correcting the external load table with the new zero pedal engine torque, that it would be better but so far no changes.

  20. #60
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    We have a 6.2L/8L90E with TSP VVT-1 cam upgrade. The long block is a 2018 and the trans is a 2015, we are using a 2015 ECM/TCM and an aftermarket harness (the fuel sensor and the Lt bank injector harness have been swapped to match the 2015 configuration). We have seen as much as -29 degrees timing at idle and it is throwing it into a default map. Local tuner is very experienced in LS tuning and has a good amount of experience with non-swap gen v tuning. Our swap is a '67 C10 and we are stuck, need to resolve this negative timing issue so that we can get started with tuning the MAF. I will include our current tune file along with a very somewhat long log file, would greatly appreciate any assistance offered. 5.2.2020_2.hpl connor's 1.3truckcoef.hpt