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Thread: Engine sputters/breaks up at 4,000 RPM.

  1. #1

    Default Engine sputters/breaks up at 4,000 RPM.

    Specs:
    454 Chevy BBC
    Holley Dual Sync distributor.
    Holley HP EFI running sequential port injection.
    Summit CDI box.

    I had the intermittent cutting out issue so downgraded the ECU firmware to V5.110. This fixed the cutting out problem.

    However, I now notice that the engine completely breaks up at 4,000 RPM regardless of load. The tach drops 500 RPM when this happens and AFR goes rich.
    I double checked rev limiter settings as well as ignition settings in the EFI and all is correct (rev limiter at 6,000 RPM, ignition parameters set to what Holley wants for Dual Sync distributor).

    At this point I'm guessing it's a coincidence it started right after downgrading the firmware, and there's a problem with either the CDI box or the distributor.

    Does this sound reasonable? Could there be some firmware or Config File issue causing this? I don't want to buy another distributor if that's not the problem. I do have a spare CDI box I can try.

  2. #2
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    1,866

    Default

    Take a System Log, so you can see the cam & crank sensors.

  3. #3

    Default

    Yeah, probably a good idea before getting another distributor. I'll try my spare CDI box first.

  4. #4

    Default

    Problem fixed. I have Ignition Output Type “Points Output Fixed Duty Cycle (MSD)” and it turns out that's broken in V5.110. I found this in the V5.130 revision log:
    Updates made to Ignition Output Type “Points Output Fixed Duty Cycle (MSD)”. If you are using this type it's recommended to update firmware. I updated to V5 Build 140 (it uses the same firmware as V5 Build 130), and now it revs fine above 4,000 RPM.

  5. #5

    Default

    Good catch. In my experience, V5 Build 140 is a really nice stable build, so that should work nice for you.

  6. #6

    Default

    I was on V5 Build 130 before V6 Build 200 that started all this. That will teach me to upgrade when it's working fine.

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