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Thread: NAG1 - Consistent limp mode on highway - 5.7 to 6.4 swap

  1. #1
    Tuner in Training Slidn's Avatar
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    NAG1 - Consistent limp mode on highway - 5.7 to 6.4 swap

    I recently got my 2011 5.7 pursuit to 6.4 swap together and found that the car will consistently go into limp mode on the freeway. If I take the car on the highway and within a mile it will go into limp mode. The car will stay locked in whatever gear it was in at the time. The car is so consistent at doing this that I can pretty much grantee that it will produce a limp mode condition in under a mile. The car appears to be fine on the street. Under load I haven't seen this issue. It only when cruising casually on the freeway.
    I thought that my tune may have been off so I used the stock 5.7 trans tune to see if I could get the same result and I did. Within a mile the car went into limp mode again. I logged the car during this process to see if we could glean any useful information.
    I also have codes P0743 - TCC Solenoid Circuit, U0100 - Lost communication with ECM/PCM, and U110B - Lost Engine Coolant Message. When this happens my speedo dies and in the VCM scanner I could see that my speed was pegged to 319.
    What could be causing this issue? Why is it so replicable. I can't tell if my tune is off or if the valve body is bad. My initial thought was that the TCM received data values that it didn't like and resorted to limp mode.

    Any help would be much appreciated.

    Here are the aforementioned files.

    Tune: 19_scat_engine_plus_SRT8_NAG1_tune.hpt

    Log of limp mode: hw2.hpl

    log of limp mode with stock 5.7 trans tune: stocktrans_6.4enginetune.hpl

  2. #2
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    Hello!
    I would suggest:
    - Step 01: check trans connection with vehicle (trans connector) - I have a similar issue and the root cause was a mis-crimped wire)
    - Step 02: Flashing the full trans tune (the files you shared are "data field" only) - so, they do not change the part of the tune which you might have issues
    - Step 03: check whole vehicle CAN communication

    Dodge Boy
    https://www.youtube.com/@dodgeboy2785

  3. #3
    Tuner in Training Slidn's Avatar
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    1) Thanks, I'll check the connector for a dirty connection and or and wiring issues.
    2) Is there a way to share the whole file? I'm aware if basic vs advance view, but not a "data field" only. Are there more parameters I need to modify?

    3) I just noticed there are some read-only parameters. Maybe I need to modify those as well? I'm guessing that may be the actual issue.

  4. #4
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    Let me know how it goes.

    No, I do not have the whole file (there are some people who offer this service - I believe German Sound does)
    A whole file size is around 9 mb (not ~1mb as HP Tuners has).

    No, not necessarily the "Read Only" parameters is the reason.

  5. #5
    Tuner in Training Slidn's Avatar
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    i went through and swapped the valve body out for a known good valve body and cleaned the trans plug. The issue continues to persist. At this point I'm thinking its either the tune or maybe the wheel speed sensors as dumb as that is. I'm really at a loss at this point.