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Thread: Question about downshifts while coasting and RPMs

  1. #1
    Advanced Tuner
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    Dec 2014
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    Question about downshifts while coasting and RPMs

    I have a question that I'm hoping someone can help answer/explain...

    I've been tweaking my shift points recently and I've noticed that sometimes when the car downshifts on it's own while coasting, that the RPMs will go up to 1300 RPMs (approx) right after the downshift (RPMs were previously at normal "idle" RPM level - around 1000 RPMs). However, like I said, it only does this someimes. Other times, the RPMs will stay around 1000 when the car downshifts while slowing down.

    After analyzing some logs, it seems that if I have the brakes applied when it downshifts, the RPMs stay at approx 1000 RPMs. If I'm just coasting when it downshifts (no brakes), that is when the RPMs go up to 1300 RPMs after the car downshifts.

    Is this "normal'? Persoanlly, I'd rather that the RPMs stay put @ 1000 RPMs after downshifting when coasting, regardless of whether I'm braking or not.

    Or does this mean that my "0 throttle" downshift speeds are a little too high?

    Not sure if it always did this and I just didn't notice it or if this is a new thing. It almost seems a little like engine braking - but I really don't want it to do that...

    Thoughts?

    Thanks.

  2. #2
    Tuning Addict 5FDP's Avatar
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    May 2012
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    Rogers, MN
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    Sounds normal to me.

    Even if it is engine braking, it's like a free service the car is doing and not using any extra fuel. I almost figure it will bump the rpm up some in case you want to get back on the gas and that way there is less lag time.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Advanced Tuner
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    Dec 2014
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    Ok, thanks... I just don't remember it doing that previously. It's kinda noticable when it does it, so I can't imagine that it always did it and I just didn't notice, but who knows.... It's probably not all that often that it downshifts without having the brakes applied, so it may not happen all that often and I just noticed it becuase I was really paying attention to the RPMs and shifts at the time (since I just modified my shift points).

    I will keep monitoring and see what happens. I've disabled DFCO recently because I hated when it did this when exiting the highway (similar effect, but much more "pronounced" - especially becuase DFCO would only be active for a few seconds, so the RPMs would jump up (to over 1500 RPMs) when DFCO kicked in and then the RPMs went right back down to 1000 RPMs a few seconds later when DFCO disabled). That no longer happens since I disabled DFCO though. At least what I'm currently talking about, after the small increase to 1300 RPMs (for example), the RPMs would then slowly drop "naturally" as I continured to slow down- instead of the sudden RPM fluctuations caused by DFCO.

    Thanks again - appreciate the input!