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Thread: VVT oscillation during cold start

  1. #1
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    VVT oscillation during cold start

    So I am seeing VVT oscillation (+/-5 degrees) during cold start/warm-up. The car is a 2015 challenger 5.7 with a 6.2 cam. What is interesting is the oscillation does not start until VSS hits 3mph and then it seems to stay even when car is not moving but idling, which I thought anything but full advance was not possible. My biggest concern is why would VVT oscillate when desired is rock steady...it's like the cam position constantly over/under shoots? Now I vaguely remember with the stock cam and tune during cold starts the car would kind of fish bite when engine was still cold but I have no logs containing cam position. I must admit in the back of my mind I was thinking...did I nick a cam bearing? I don't have the log on hand but can post it up and the tune (work in progress) when I get home. The plan was to get the car dyno tuned by a pro but still struggling to find a shop in Chicago land area that doesn't tune for "off road" use only, meaning I need to pass emissions. Anyways, just thought I would ask if you guys have seen this behavior before? I never did a cam/crank varition relearn when I installed the 6.2 cam so wonder if that is the problem?

    Nevermind, I think I know what the problem is...in my infinite wisdom I copied over the cam training values from the 6.2. We'll see when I get back to the garage later today.
    VVT oscillation.JPG
    Last edited by Homer; 05-21-2020 at 12:54 PM.

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    Well this morning I reverted the training values back to stock (forgot to clear adaptives though) and same oscillation but this time the car was never moved. Seems like catalyst heating starts to move the cam just about a minute after cold start and once the ECT hits ~190F normal cam table takes over. Just did the crank/cam relearn so after work I'm going to try to see if I get the same result (going to clear adaptives this time before start-up).
    Last edited by Homer; 05-22-2020 at 10:20 AM.

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    So the crank/cam relearn seemed to improve the oscillations but I still have it but it decays. If my 5.7 JGC does not exhibit this I am thinking that maybe my cam sensor might be flaky?

    cam relearn.JPG

  4. #4
    What is the crank/cam relearn ?

  5. #5
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    It's available on alfaOBD (does not work with HP tuners dongle). Alfa is a diagnostic/scan software...IMO alfa and HP go hand in hand. It can also allow some car configurations to be changed in the BCM like Zautomotive's Tazer. It's the software that helped me enable launch control on my non-STP equipped RT.

    https://www.alfaobd.com/

    relearn.JPG

  6. #6
    Quote Originally Posted by Homer View Post
    It's available on alfaOBD (does not work with HP tuners dongle). Alfa is a diagnostic/scan software...IMO alfa and HP go hand in hand. It can also allow some car configurations to be changed in the BCM like Zautomotive's Tazer. It's the software that helped me enable launch control on my non-STP equipped RT.

    https://www.alfaobd.com/

    relearn.JPG

    Thank you . I was actually looking into this very product .

  7. #7
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    Just out of curiousity anyone know what would be a symptom of a nicked cam bearing on VVT cam position?

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    Still have no clue what causes the exhaust cam to oscillate when engine is cold. Swapped the cam sensor from my 2013 JGC, did a cam/crank relearn and same darn thing. Could it be the VVT solenoid build up or something? BTW I added the catalyst heating status PID and it never changes from "not enabled" so not sure what causes the cam to move during idle at about a half a minute after start-up?

  9. #9
    Can you post a tune and a log ? Also when copying over the values from a stock cam timing of a 6 you should subtract 9 degress from the entire table to align everything together

  10. #10
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    I honestly don't think it is the tune. I remember the car having a fishbite feel to it during cold starts when it was stock.

    Here is a log (did not have the WB or fuel pressure sensor connected to the pro-link) I took the other day after messing with the air tables.
    Oscillation.JPG
    The exhaust cam tables were copied from a 2015 6.2 manual but I did offset the values by 9 degree, the norm/base table follow WOT.

    cam tables.JPG

    I never really intended to do the entire tune myself (don't have the time, patience, open roads and skill set to do it) and had planned to get a pro dyno tune it but not terribly confident in the shops in my area (Schaumburg, IL) when it comes to FI non-HC tuning. Car runs fine but only sees a 14 mile round trip commute through stop and go traffic a couple of days in a week. I will say the airflow tweaks Hemituna posted in a different thread is pretty impressive...throttle is very lively now.

    6-27-2020 air tables.hpt
    Air tables 6-28-2020.hpl

  11. #11
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    It's clearly oil temperature dependent, so why not delay enabling VVT until higher temps? The position controller may not be so friendly with the different friction load while its cold. The actuator controller loop gains themselves are likely not calibratable.

    Capture.PNG

  12. #12
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    Probably is set too low....I use 900 rpm generally so cam is stable till revs rise - regardless of VSS

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    Quote Originally Posted by smokeshow View Post
    It's clearly oil temperature dependent, so why not delay enabling VVT until higher temps? The position controller may not be so friendly with the different friction load while its cold. The actuator controller loop gains themselves are likely not calibratable.

    Capture.PNG
    Ah..good point. BTW those are the stock values. Also logged my 2013 JGC 5.7 and it does not exhibit this behavior but it does have VVT enable around 1000 rpm. Comparing when the oscillations finally go away, oil temp is ~154F. Will try running the 6.2/6.4 manual trans settings. Also might try 0w40 oil. There was an old TSB or Star# that recommended 0W40 on manual 5.7s to quiet down the valves...not my issue but shows it won't have any ill effects if FCA suggests it.

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    Quote Originally Posted by Hemituna View Post
    Probably is set too low....I use 900 rpm generally so cam is stable till revs rise - regardless of VSS
    Those were the stock values but if I look at and 2015 5.7 auto the settings are significantly higher. Even 2015 manual 6.2/6.4s have them higher. I'll give it a go. Thanks guys!

  15. #15
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    I think that was it. Just did a cold start and drove the car around and no oscillation. Wonder why the stock values were so low to begin with?

  16. #16
    I'm in the disvovery process of my Tune and this post had me curious. I had it professionally tuned but I am taking it from here. I have a few more classes to get through before I try to tweak anything further. So to that point. Would you be able to tell me what having the enable RPM settings set to the following accomplish? Is there a chance my tune didn't scan in correctly?
    Attached Images Attached Images
    Last edited by McCloud; 07-08-2020 at 04:44 PM.

  17. #17
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    Quote Originally Posted by McCloud View Post
    I'm in the disvovery process of my Tune and this post had me curious. I had it professionally tuned but I am taking it from here. I have a few more classes to get through before I try to tweak anything further. So to that point. Would you be able to tell me what having the enable RPM settings set to the following accomplish? Is there a chance my tune didn't scan in correctly?
    Could be you have a big cam requiring VVT to be disabled?

  18. #18
    Quote Originally Posted by Homer View Post
    Could be you have a big cam requiring VVT to be disabled?
    That crossed my mind, I wonder if that is better than disabling it in the following table.
    Attached Images Attached Images

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    My JGC has all of them disabled in stock form and it is not modified with VVT working, maybe it was enabled to actually disable it?

  20. #20
    Quote Originally Posted by Homer View Post
    My JGC has all of them disabled in stock form and it is not modified with VVT working, maybe it was enabled to actually disable it?
    I did a compare with my stock file and it has the same setup as your JGC. I wish I could find documentation on the PCM that describes how the tables are coded/interact. It's is going to take alot of trial and error to figure these things out.