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Thread: Need some advice on tuning cruise speeds at 75 mph and up

  1. #1
    Fuel Injected!
    Join Date
    Feb 2013

    Need some advice on tuning cruise speeds at 75 mph and up

    I've not done a whole lot of tuning in the 2500 rpm/75+ mph range as I don't drive it very often.

    This weekend, I drove to a buddies house about 45 miles away. On the way home, cruising about 78 mph is when I'd see knocks accumulating at a rate of the count increasing about 1 per second.

    If I recall, BLM in the area in question is close. Wideband o2 sensor stayed pretty much around the .98 and 1.02 range.

    As I was driving, and as knock count kept increasing, I dropped the areas where knock was occurring in the main spark table down 10 degrees and saw no change in the count increasing one per second. I also did not notice any change in how the engine ran.

    Attached is the bin file and log for the 1228062 ecm.

    One question that I don't recall was ever cleared up, is the knock count that is reported in the data stream 1 count per 1 detected knock, or, 1 count for every 256 knocks?


  2. #2
    Super Moderator
    Join Date
    Mar 2011
    Camden, MI
    with most datastreams, the knock counter displays the MSB of the accumulated amount of time that the knock filter indicates that knock is occurring. the filter has a finite reaction speed to both indicating when knock is occurring and when it indicates that it isn't... I remember one of the genius Aussie guys playing with a filter using a scope and a function generator, revealing pretty interesting characteristics about just how it acts in a lot of scenarios, some being that he was simulating knock both starting and stopping before the filter actually reacted and signaled to the microcontroller what was going on.

    dropping 10* out of advance should have produced a noticeable change in engine output, but I guess it would depend on how much timing the knock sensor/filter is removing as well.... if the sensor wants 15* out to keep it happy, removing 10 from the table would still cause 5* of KR to be applied to keep the sensor/filter happy.

    sounds like false knock to me though. 10* is a lot of timing for there to be no change in knock accumulation rate.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E

  3. #3
    Fuel Injected!
    Join Date
    Feb 2013
    I'm going to have to run the log again, but as I recall, I would have thought that there would have been a somewhat noticeable change in how the engine was running with 10 degrees removed.

    Will also have to remember to look at the timing table for the original P66 bin used on that engine to see what that table looks like.

    I wonder if it could have been that the sensor/filter wanted 10 removed and I just happened to remove ten and that's why there wasn't a difference in performance....?....

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