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Stop light surging, lurching??

Discussion in 'Gen 3 Prius Technical Discussion' started by Hybrid_Motorsports, Aug 31, 2024 at 8:34 PM.

  1. Hybrid_Motorsports

    Hybrid_Motorsports New Member

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    I just got my 2014 and still getting used to my first hybrid but today I felt something strange. I was stopped at a red light in EV mode with the engine shut off and while holding the brakes, I could feel just a slight lurching like something behind me trying to push the car while I hold the brakes. It's hard to explain, its like the feeling when you let off the brake and the car moves forward but it was trying to do it when I was holding the brakes. it was very faint and I barely noticed it for a few seconds until the light turned green. I was never able to reproduce it and I'm questioning my sanity if it was just heavy wind pushing on the car..

     
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    What’s the miles on it?
     
  3. ChapmanF

    ChapmanF Senior Member

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    The engine has a good bit of rotating mass, and the torque to start or stop it often comes through the transmission a little and rocks the car a bit.

    The car makes heroic-ish efforts to keep that rocking to a minimum—if you're parked in a gen 3 with your foot off the brake, you can even hear the car apply the brakes for you an instant before it cranks or stops the engine, just to restrain the motion as much as it can. They also can use MG2 to apply a countertorque trying to hold the car still while MG1 cranks or stops the engine, and they try to pass very quickly through the low-RPM range where the engine resonates with the car body.

    Still, despite all the efforts, you notice the lurch sometimes. Maybe we should just smile and remember how hard they worked to make it not worse.
     
  4. Hybrid_Motorsports

    Hybrid_Motorsports New Member

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    It's a 2014 CT200h with 115k on it. I got it a month ago and already did all the major services. Took out the entire EGR cooler/valve and made them spot less along with the intake manifold. Added a catch can while I had everything apart.

    i changed the ecvt fluid, it wasn't very dirty but I always change all the fluids when I get a used car. The hybrid battery fan had minimal dust on it which gave me some relief for the battery life.
     
  5. Hybrid_Motorsports

    Hybrid_Motorsports New Member

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    I understand that but the engine was off and not close to starting. I was just sitting at the red light in EV mode with my foot on the brake and could feel this back and forth motion.
     
  6. ChapmanF

    ChapmanF Senior Member

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    If you had the animated-car display showing, did any arrows from the electric motor to the wheels appear and disappear while you were watching? If you have an OBD device that can show live data, were there any changes to MG2 torque while you were stopped?

    The car is programmed to apply a small amount of MG2 torque while stopped, to create the same feeling as an auto-transmission car with the engine idling. To waste a little less electricity, it stops doing that if you are pressing the brake pedal hard enough, but it resumes the slight force if you let up a little on the pedal pressure.

    if you're applying pedal pressure right around that threshold, you could notice the MG2 torque coming and going, and you would see same on an OBD scanner or the power-flow arrows on the dash.

    (Note, both an OBD scan tool and the dash display get that information by sending repeated queries on the car's network and getting answers back, which means what you see on the display can lag a little bit behind what you feel happening.)