2011 Prius poor fuel economy after hybrid battery replacement etc

Discussion in 'Gen 3 Prius Fuel Economy' started by ilovetoracecross, Dec 26, 2017.

  1. ilovetoracecross

    ilovetoracecross Junior Member

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    Hi all. Follow up from last months debacle.

    Replaced the hybrid battery after a huge debacle at the dealership with a greenbean refurb'd battery.
    Replaced fuel pump as well, as that was the actual problem with the vehicle, despite the dealership claiming it was the hybrid battery.. At the same time, I replaced all the spark plugs, cleaned the air filter, changed the oil, and cleaned out the MAF.

    Stuff has been pretty good! Except..... Mileage. And I remember the first tank post work was near 500 miles to go, then it sort of snuck down over the last month to..420 or so.

    Using the Trip A setting and the computer mileage, the car only gets 38mpg.. Typically I drive the LIE here on lawn guyland for work appointments, so I do a LOT of highway miles. Typically I set the cruise control at 70, jump in the HOV lane, and voila.
    Currently I'm driving with a full tank of gas, heater on, fully inflated tires, relatively cold (above freezing), and did two 50 mile highway trips on the LIE today. Average was 38.2. I currently buy premium fuel, and am under the impression it's 10% ethanol, since thats all we have here...

    I did clean the MAF today prior to the trip. No real effect. Still sits down at 38.
    I could diagnose the MAF sensor I guess, or just get one from my parts provider (I am a mechanic, but not a modern car mechanic), but would love to hear some ideas from others before I start burning what little free time I have to think this out. Thanks
    Myles
     
  2. TMR-JWAP

    TMR-JWAP Senior Member

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    Although I don't have all the answers, I feel confident saying you are unnecessarily spending extra money on premium fuel. Higher octane fuels merely have chemistry to prevent pre-ignition in higher compression engines. Many times this also results in a slower flame front propagation during the "power" stroke of the engine. Unless your car specifies "premium fuel only" then all the car needs is regular unleaded. The car engine is designed to operate most efficiently with the fuel recommended in the owners manual, which I believe is regular ol' 87 octane unleaded.

    Also, I've noticed I'm down about 5 mpg since the weather turned colder.
     
    #2 TMR-JWAP, Dec 26, 2017
    Last edited: Dec 26, 2017
  3. Dxta

    Dxta Senior Member

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    What's the mileage on her?

    How were the spark plugs, and all that, when you replaced them?

    If you've got tech stream, or torque pro, try checking the voltage blocks of individual batteries to see how they fizzle out.

    Some rrfub packs aren't that cool. I'm not saying what you've got is a crab though.

    Dxta
     
  4. bisco

    bisco cookie crumbler

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    what were your mpg's previously?
     
  5. ilovetoracecross

    ilovetoracecross Junior Member

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    We analyzed the old pack. Definitely had some bad cells. Have not analyzed new pack.

    First tank of gas post repair nearly 80 miles more. Now the indicator barely crosses 420.
    208k on it.

    Compression ratio is like 13:1, no? That (at our shop) is well past the limit of regular...?


    Pixel ?
     
  6. CR94

    CR94 Senior Member

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    That's the expansion ratio.
     
  7. tpenny67

    tpenny67 Active Member

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    The effective compression ratio is much lower due to the intake value staying open so long and is in the 6:1 to 8:1 range and varies with the valve timing. I can't find the actual compression ratio numbers, but there's a neat chart of the valve timing here. The intake valve can close after the piston is halfway back up the cylinder.
     
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