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ICE races with no load going downhill

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by RobertO, Feb 21, 2004.

  1. RobertO

    RobertO New Member

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    I'm hoping this has nothing to do with the (I call it) recall for the ECU work that was done to my car last week:

    I was going down a long, winding hill at about 35-40 MPH, 99.9 MPG indicated (normal), NOT in "B" mode, when the ICE sudennly starte and racee up to very high RPM (higher than I've ever heard it).

    It stayed there until I applied the brakes at a stop sign.

    What do you thing THAT was??

    bpb
     
    #1 RobertO, Feb 21, 2004
  2. miniracer

    miniracer New Member

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    This probably ought to be in a different forum, eh?
     
    #2 miniracer, Feb 21, 2004
  3. efusco

    efusco Moderator Emeritus
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    Brake on, off, or what? Did you check the battery SOC? Do you think it could be the engine doing a little B-mode of it's own to prevent the motors from over RPMing?

    That's pretty curious, but I doubt that it has anything to do with the 'recall'.
    --evan
     
    #3 efusco, Feb 21, 2004
  4. RobertO

    RobertO New Member

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    Well, it was normal driving.

    I've gone down that hill many times in normal regen mode with the 99.9 MPG indication and current flowing to the battery on the monitor. Same speed range of 35 - 40 MPH. ICU never comes on.

    This time, I do recall that, for the first time ever, the battery was showing all green bars.

    Within a minute of pulling on to the freeway, the battery charge level indicator was back to one white bar at the top - the usual max load.

    since Prius needs no tach, I couldn't tell you the RPM of the ICU when it kicked in - just that it was as though it was in the equivalent of 1st or 2nd gear - really revving high going down the hill.

    I couldn't really feel any compression braking from the engine. Probably due to the Hybrid Drive taking readings from the regen as I went down the hill.

    I'll talk to the dealer guys next week - not that they'll know more than any of us.

    Meanwhile, the car is running just fine since then. Who can say what that was? Not I.




    Bob
     
    #4 RobertO, Feb 21, 2004
  5. Tempus

    Tempus Senior Member

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    I've heard that the System doesn't let the battery get overcharged, and if it needs to it will 'bleed off' battery charge by a number of methods, including, for example, a couple of start/stop cycles sitting at a light.

    If you were picking up too much juice, and the battery was already full, I could see it doing something like spinning the ICE with the Motor just to burn off some.

    Over a certain speed, doesn't the ICE really just free-wheel with no combustion when it's 'off' anyway?

    I thought I heard that over a certain speed, the ICE couldn't really be 'off' as in stationary crank, they just opened the valves and let it spin when it wasn't needed.

    Since you weren't feeling any compression it makes me think even more that might be what it was. Interesting.
     
    #5 Tempus, Feb 21, 2004
  6. efusco

    efusco Moderator Emeritus
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    I bet that's it, the ICE was bleeding off excess charge from the HV bat....If you've got time next week it probably wouldn't hurt to have the service dept check it out, but I bet everything's ok.

    Let us know what you learn for sure.
    --evan
     
    #6 efusco, Feb 21, 2004
  7. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    I've experienced the same thing coming down a large grade. It's not quite as high as "B mode", but it is the ECU's way of providing the same off pedal braking effect when the HV battery is at the upper limit of it's SOC.

    I'd consider it completely normal.
     
    #7 HTMLSpinnr, Feb 22, 2004
  8. Tempus

    Tempus Senior Member

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    Sounds like a job for the EV Mode Button, so you can run the battery down just before the top of the hill, and not waste any of that prescious energy on the way down :)
     
    #8 Tempus, Feb 22, 2004
  9. ammiels

    ammiels New Member

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    Wayne, the wonderful, has shown this may happen if gas/fumes spill over into the charcoal canister and the system purges itself, more likely after fueling. In any event the effect is harmless to the car.
     
    #9 ammiels, Feb 22, 2004
  10. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    This would happen more after accelerating just after startup.

    As for EV - that button only works under 30mph.

    This "revving" condition only occurs coming down hills at highway/freeway speeds when SOC is at it's upper limit. EV wouldn't help here, and the canister and/or vapors would most likely have been purged by this time (an event that happens shortly after startup).

    Also, at highway speeds above 50mph, the ICE must spin in order to prevent MG1 from overreving. In the classic Prius, that was 42mph, in the '04, it's closer to 50-52mph. After that, you get "warp stealth" (ICE spins only as fast as it needs to in order to prevent overspin in a low-load situation).
     
    #10 HTMLSpinnr, Feb 22, 2004
  11. Tempus

    Tempus Senior Member

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    He said he was coming down a long winding hill at 35-40, probably with some braking too.

    My comment on the EV Button was that he could have gone to EV on the upslope before the crest to run down the HV and save some gas and hit the top of the hill with room for some of that lovely regen he was getting going down.

    One of those situations where 'looking ahead' could help.
     
    #11 Tempus, Feb 22, 2004
  12. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    EV still wouldn't help - it doesn't allow continuous high current drain - regardless of SOC.
     
    #12 HTMLSpinnr, Feb 22, 2004
  13. RobertO

    RobertO New Member

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    All:

    Thanks for the cogent feedback.

    I'm inclined to agree that it's some sort of energy bleed off thing.

    Haven't seen it in the Owner's Manual - maybe I missed it. If it's not in there, it's certainly something that should be. If you'e never heard the ICE race, you'll never forget that sound. Makes one think that a belt or shaft has snapped and the engine is running ungoverned.

    I'll for sure let you all know what the Service Advisor tells me tomorrow. Hopefully, it will make sense, and be the truth. One never knows, with the '04, if they really know, or as Bill Maher says, "...they make shit up...".

    Drove the car to meet our kids and grandson for breakfast this morning; smooth as silk, nothing abnormal.

    Love this car.

    Have a great Sunday afternoon, all.


    Bob
     
    #13 RobertO, Feb 22, 2004
  14. daniel

    daniel Cat Lovers Against the Bomb

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    Even without going into full EV mode, it would be nice to be able to instruct the car to draw down the battery SOC (saving some gas) in anticipation of a high regenerative situation coming up.
     
    #14 daniel, Feb 26, 2004
  15. RobertO

    RobertO New Member

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    Well, here3 it is, 2 weeks later and they still don't have an answer.

    They tell me "Toyota is still reviewing the symptom".

    Z-z-z-z-z-z-z...


    Meanwhile, it has not happened since.


    Go figure.


    Bob
     
    #15 RobertO, Mar 19, 2004
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