Pulsation when "half-coasting" on Cruise

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by TheLandYacht, Oct 1, 2020.

  1. TheLandYacht

    TheLandYacht Member

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    New-to-me 2010 Prius III, first time P= owner.

    I'm wondering if this is a normal thing, or something I should have checked...and if it's something anyone else has experienced.

    On Cruise Control at highway speeds, when "sort of" coasting, I get a pulsation reminiscent of the feeling when your ABS would engage while braking hard (obviously without the hard deceleration)...that grab-and-let-go, grab-and-let-go feeling at about half-second intervals.

    This is while it's doing what I will call "sort-of" coasting, meaning (to me) where your MPG "gauge" is in the 75mpg-ish range, so not maxed out. Like you're on a very slight decline. ONLY happens (so far that I've noticed) at highway speeds. Does NOT happen (that I've noticed) when it's right at the 50-mark, or maxed-out at the 100-mark.

    Is this normal? If not, should I be concerned? I find myself being hyper-aware of "unusual things" since I've never owned a vehicle of this type before...and I've only owned it for a couple of days.
     
  2. Maarten28

    Maarten28 Active Member

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    I've had a similar experience with a normal car, also on cruise, also going slightly downhill. My explanation there was that it could not handle well the region where it would coast and had to use a little fuel.
    Maybe the throttle body needs checking?
     
  3. TheLandYacht

    TheLandYacht Member

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    I'll give that a look/thought.

    I would have thought this symptom would show up under load/etc...or if not, that I wouldn't "feel" it in the drive-train (where I could feel it effect the way the vehicle rolls).

    To clarify, I can feel the vehicle sort of "jerk" rolling down the road (down the rather long slight inclines, of which there are a lot where I commute to/from) again, as tho the brake (in a normal car) were being tapped at half-second intervals.

    My thought is...this is something to do with P='s brain. Like P=s brain is saying "should I push this energy into the battery or not?" since it happens only when the car is "sort of" coasting (when the MPG gauge is somewhere around 3/4 of the max line)...and goes away if it goes all the way up (or back down to the half-way point).

    BTW, I've decided on a name for the new (to me) Prius...The wife has gotten us into the habit of naming our vehicles. For instance my last vehicle's name was Irene Cara(van). Care to guess what it was?

    Anyway, this one will be my Toy(Yoda)
     
  4. TheLandYacht

    TheLandYacht Member

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    Update on this symptom, which hasn't changed significantly since I initially reported it in October.

    Shortly after the initial message(s), I got my hands on a little bluetooth OBDII reader & use TorquePro continuously for anything but very short trips.

    Anyway, one of the "Gauges" I use is the RPM's.

    I note that the symptom happens at any speed from 20 all the way up to highway cruising speed...but ALWAYS at the same RPM's. That RPM range being 1500-1600rpm.

    Just so happens that RPM range is pretty much exactly the RPM range needed to keep the speed constant on a level surface, which is annoying
     
  5. wheezyglider

    wheezyglider Active Member

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    I assume you can reproduce the symptom without using cruise, by watching RPM on Torque app and keeping in that 1500-1600 range? Under normal driving, does your car have a perceptible kick whenever the ICE comes on as it switches out of pure EV? [I don't know enough myself to diagnose your symptom, just wondering if it's related to something more common.]
     
  6. TheLandYacht

    TheLandYacht Member

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    no perceptible kick...and yeah, reproducible off cruise
     
  7. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I can't be certain, but I think you are describing the natural roughness of a four cylinder engine being operated at low RPM.

    1500rpm / 60 seconds is 25Hz. A low vibe you mostly feel instead of hear.

    The car's automation is trying to run the engine as little as possible, at the lowest RPM necessary, with the throttle open as far as possible.

    Those conditions will generally lead to the lowest fuel consumption- but a wide open throttle at low RPM also brings out that roughness.

    So I can't be 100% certain that's what you're feeling, but I thought I'd point out that I've felt it in every Prius I've ever driven, and there's a good reason for thinking you're feeling some rumble down there.

    Almost as if a computer in the background was ruthlessly manipulating the gear ratios of the CVT to keep that car in that specific operating condition? Hmm, funny that....

    That's (probably) your savings building up that you're feeling.

    We used to call this "lugging" in manual shift cars of an earlier age. It was generally to be avoided, because in some engines it could cause undue wear. But some engineers figured out that it was actually a very desirable operating regime for fuel savings, so things have been optimized to support operating 'heavy and slow,' as it were.

    Electrification brought a lot of fuel savings to the Prius, but it should be understood that quite a lot of the efficiency gained is from a gas engine under complete computer control, being made to do weird things that a human operator would not normally choose.
     
    #7 Leadfoot J. McCoalroller, Mar 14, 2021
    Last edited: Mar 14, 2021
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  8. TheLandYacht

    TheLandYacht Member

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    Never been in a normal vehicle that "lugged" in the manner you're describing.

    I have, however, been in an 18-wheeler when the "engine brake" got engaged...and the sensation is eerily similar (except for the lack of deceleration). And if you've been in one, THAT is the sensation I'm describing.

    I know the concepts are likely not even close to being similar, but that's what it feels like. Like the whole vehicle is shuddering at half-second intervals.
     
  9. TheLandYacht

    TheLandYacht Member

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    I noted the mechanic mentions (toward the beginning of the video) the vehicle came in with a noticeable "shudder". I'm wondering if my symptom is what he's referring to.

     
  10. TheLandYacht

    TheLandYacht Member

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    If it does end up being that tranny, looks like I can source a replacement pretty damn cheap. What should I expect from a local shop for installation? I hope not as much as your average tranny-swap, since it looks considerably easier from other videos.
     
  11. ASRDogman

    ASRDogman Senior Member

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    Don't replace the whole transmission, that the customer paid for probably, just the MGU.
    Don't worry about that "O" ring, why replace it with a new one since it's so easy to do?
    I wonder if they found out why it fried? Did the coolant pump fail and the fluid over heated?
    mmmmmmm
     
  12. TheLandYacht

    TheLandYacht Member

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    a "fry" of that nature is electrical...got enough e background to recognize short-scorch.

    someone in one of the threads mentiond thats why it's important to go with Toyota fluid, others will eat the insulation...leading to exactly this result
     
  13. ASRDogman

    ASRDogman Senior Member

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    "I" know that... That's why I wondered if they bothered to check as to WHY it happened?
    Was it the wrong fluid that eventually caused it? And damage to the other motors?

    I know it was just a video of changing "that" part, but it would have been nice if they had said why
    they thought it had went bad.

     
  14. TheLandYacht

    TheLandYacht Member

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    An interesting wrinkle I should have noticed a LONG time ago but...

    The symptom doesn't happen with a cold engine/tranny, even if I "let it warm up" first (I don't pull out of the driveway til Coolant Temp is over 100 degrees).

    For the first 5 minutes or so of a drive, it's smooth as silk at any RPM. Then it's like a switch gets thrown, it doesn't "come on gradually"

    Does that mean anything to anyone?
     
  15. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Can you correlate the timing to anything else? Maybe monitor open loop vs. closed loop fueling on your device, see if the roughness comes in with the programmed changeover to closed loop?
     
  16. TheLandYacht

    TheLandYacht Member

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    Not sure how or what I'd monitor to find that out. Any pointers?

    ...again, using a bluetooth gizmo & TorquePro with (theoretically) the most recent list of PIDs I found somewhere on Priuschat (can't remember where)
     
  17. TheLandYacht

    TheLandYacht Member

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    I've got a 40mile commute home from work in a bit over half an hour, so this is the perfect time to give me something to watch (or watch for)
     
  18. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    The PID I'm describing is one of the base enumerated ones. In open loop, the car is doing a "spray and pray" method with the fuel injection, blindly hosing gas in there on a predetermined program to try and get things nice and hot. After a certain temp threshold is hit, the car switches to closed loop where the fueling is closely controlled by whatever the O2 sensor data returns for recent combustion efficiency. Then it runs in that feedback loop forever.

    Most apps or tools have direct access to show this flag.

    I've never used torque pro but I'm sure it's in there somewhere.

    I usually read it on a hardware OBDII Scangauge device
     
  19. TheLandYacht

    TheLandYacht Member

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    Can anyone with more experience with TorquePro weigh in with which PID Leadfood is talking about? I've been all the way through the list & don't see one like the one(s) described at the beginning of his post .

    Service 01 PID 03
     
  20. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Somebody figured it out in this forum post. Looks like you can do it via custom pid entry.

    I'm kind of surprised it isn't a lot more available. A lot of fuel injection troubleshooting starts with this.
     
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