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Mysterious misfire ONLY when low HV battery, but No DTC’s

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Baz2473, Jan 23, 2019.

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  1. Baz2473

    Baz2473 Junior Member

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    Hey all. Has anyone else encountered the random, mysterious misfire that only sometimes happens and only ever when the HV battery is low and never throws a single fault code?

    Here’s a little background info on the car.
    2015 last of the gen 3’s
    196,000 miles.
    No loss of oil or water.
    Never ran low on oil.
    Regular services.

    At 195,000 it developed the famous engine knock on startup along with this new mysterious misfire (or at least it feels like a misfire)!

    Stripped out the entire egr system. (Cooler, valve, Pipe & intake manifold) cleaned throughly, replaced the PCV valve, introduced an oil catch can, removed and ultrasonic cleaned the fuel injectors. Replaced all 4 spark plugs. All had no effect on the misfire but did cure the startup knock...

    Anyone have any ideas or experience with this? Any help would be appreciated.
     
    #1 Baz2473, Jan 23, 2019
  2. JC91006

    JC91006 Senior Member

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    Many have reported the low SOC misfire. Has the car overheated before? Failed water pump/inverter pump?
     
    #2 JC91006, Jan 23, 2019
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  3. Baz2473

    Baz2473 Junior Member

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    Never overheated and no apparent problems with either pump.
     
    #3 Baz2473, Jan 23, 2019
  4. bisco

    bisco cookie crumbler

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    plugs, injectors, throttle, maf?
     
    #4 bisco, Jan 23, 2019
  5. Baz2473

    Baz2473 Junior Member

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    New plugs. Ultrasonic cleaned injectors, maf untouched.?
     
    #5 Baz2473, Jan 23, 2019
  6. JC91006

    JC91006 Senior Member

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    So basically you can drive the car trouble free as long as the battery SOC does not go to 2 bars? When I read about this problem 2 years ago, I couldn't figure out how the low SOC would do that to the engine. 2 years later.....I'm still unsure...............

    I did buy a car with the low SOC misfire problem, but that car also had a bad head gasket, that was repaired using some coolant additive. Long story, that car was sold before I even registered it to my name.
     
    #6 JC91006, Jan 23, 2019
  7. Baz2473

    Baz2473 Junior Member

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    That’s correct. It runs like a dream unless that battery is under the half way mark. The lower it is the worse the misfire?
     
    #7 Baz2473, Jan 23, 2019
  8. JC91006

    JC91006 Senior Member

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    So the remedy is to not let the car SOC get low. I would recondition the battery now and get it as strong as possible. Then whenever you're at a stoplight and you see the SOC drop low, do a force charge on the car and get the SOC back up (only take 30 seconds or less)
     
    #8 JC91006, Jan 23, 2019
  9. JC91006

    JC91006 Senior Member

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    I know you cleaned out the EGR valve, I wonder would replacing it help? It's not hard to get to (much easier than the damn cooler)
     
    #9 JC91006, Jan 23, 2019
  10. Baz2473

    Baz2473 Junior Member

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    That is what I currently do, I was just hoping that there was a permanent fix rather than messing around like that can’t afford a new hybrid battery...
     
    #10 Baz2473, Jan 23, 2019
  11. Baz2473

    Baz2473 Junior Member

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    Was thinking this myself but wasn’t sure if that could be the reason for the misfire? Do you know if unplugging it would be a way of testing if this would cure it. (If I unplugged it when the valve was closed) ?
     
    #11 Baz2473, Jan 23, 2019
  12. JC91006

    JC91006 Senior Member

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    I'm going to have to defer to some of the guys that knows this stuff better, I don't really know the answer......in 24 hours, you'll get get some more responses.
     
    #12 JC91006, Jan 23, 2019
  13. tankyuong

    tankyuong Senior Member

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    Mine did the same and finally blew a hole in the engine 2 months later
     
    #13 tankyuong, Jan 23, 2019
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  14. Mendel Leisk

    Mendel Leisk Senior Member

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    Where was the hole; did you figure out what failed?
     
    #14 Mendel Leisk, Jan 23, 2019
  15. tankyuong

    tankyuong Senior Member

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    The hole was in the block, replaced the engine
     
    #15 tankyuong, Jan 23, 2019
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  16. bisco

    bisco cookie crumbler

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    rings?
     
    #16 bisco, Jan 23, 2019
  17. Baz2473

    Baz2473 Junior Member

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    Thank you for your help.
     
    #17 Baz2473, Jan 23, 2019
  18. Raytheeagle

    Raytheeagle Senior Member

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    What are you using to read codes?

    Have you tried moving the coils around and see what happens?

    Still got the old plugs for comparison?

    No lights on the dash?
     
    #18 Raytheeagle, Jan 23, 2019
  19. Baz2473

    Baz2473 Junior Member

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    Techstream to read codes. (There is none)
    Swapping coils around made no difference.
    Yes still have old plugs. (See attached pic)
    No warning lights what so ever.
     

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    #19 Baz2473, Jan 24, 2019
  20. Baz2473

    Baz2473 Junior Member

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    Ok. So I’ve decided to take off the entire EGR system again including cooler and IM and give it a through ultrasonic clean. Hopefully this will help. ?
     
    #20 Baz2473, Jan 26, 2019
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