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Sudden drop in MPG, and I can't figure out why.

Discussion in 'Gen 2 Prius Fuel Economy' started by apinson34, Sep 4, 2012.

  1. apinson34

    apinson34 Junior Member

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    Here's the Dilemma guys.

    I recently (as in the last two months) Have only been getting an average of 43.2 MPG. This average is from filling up the tank and from the MFD, (MFD is about 42.6).
    Another symptom is almost everytime I start my car (with the A/C) my Traction battery dies within the first two minutes.

    I haven't done any driving style changes, as I used to average 48-53 MPG.

    But I have done a few service things to the car recently. Any help would be appreciated.

    Here's the following changes that have occurred in the past six months:

    1. Transaxle fluid change, Done at 72k miles. Didn't affect gas mileage at all.
    2. Coolant Belt Change (As Toyota refers to it as the timing belt) (changed at 78k)
    2. New Tires. Fuzion Touring Tires, 4 New. These didn't affect gas mileage. (Although I miss the handling of my Toyo Extensa A/S) (Changed at 83k) They are at 40 psi on the front, 38 on the back.
    4. Changed the spark plugs, I got the Bosch Pregapped Iridium. (changed at 90k)

    I put synthetic oil every 7500 miles. I also get the best Oil Filter, and put a Fuel Injector Cleaner (Techron from Chevron Fuel System Cleaner) I only use Chevron Regular gas. Should I fill up with Plus to see if that helps? I also change the air filters (including the cabin) every other oil change.

    I have also cleaned the throttle body and the MAF Sensor. The sensor still had an amber color and the throttle body wasn't that dirty.

    There have been a few suggestions. One was to check the A/C (which I have noticed lately that the compressor runs more.) The other was to check the 12 volt, I did the MFD test and after letting the car sit for a while and turning to "on" position, with the headlights on. It brought it down to 11.6 volts.

    I'm just frustrated because my mother owns a Prius a year older than mine. I take the same driving style from my car. and her's gets 52 MPG.


    Any help would be appreciated guys!


    Thanks,

    Alex.
     
    #1 apinson34, Sep 4, 2012
  2. John H

    John H Senior Member

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    #2 John H, Sep 4, 2012
  3. bisco

    bisco cookie crumbler

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    at what point in all this service did the mileage drop and how many miles/gallons has it been going on for?
     
    #3 bisco, Sep 4, 2012
  4. PriusCamper

    PriusCamper Senior Member

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    Your car doesn't have enough 12volt battery power to run properly... It's hungry and confused... It's trying to use other sources of power to make up for the loss and the car can't get good MPG that way! If you find a good deal on a yellow top 12v battery let us know about it!
     
    #4 PriusCamper, Sep 4, 2012
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  5. richard schumacher

    richard schumacher shortbus driver

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    Most likely the non-LRR (low rolling resistance) tires. Increase their pressures to the maximum given on their sidewall for the front two, and 2 PSI less for the rear. Higher octane gas will do nothing except drain your wallet faster.
     
    #5 richard schumacher, Sep 4, 2012
  6. jadziasman

    jadziasman Prius owner emeritus

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    I would suspect an potential issue with the Bosch spark plugs. Check for a misfire at the tailpipe with the ICE running. Even a sporadic misfire is enough to cause a 10% drop in mpg. This is easy enough to check. Buy four new NGK iridium plugs to see if your mpg returns to what you had been getting.
     
    #6 jadziasman, Sep 4, 2012
  7. jadziasman

    jadziasman Prius owner emeritus

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    upload error
     
    #7 jadziasman, Sep 4, 2012
  8. jadziasman

    jadziasman Prius owner emeritus

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    #8 jadziasman, Sep 4, 2012
  9. jadziasman

    jadziasman Prius owner emeritus

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    #9 jadziasman, Sep 4, 2012
  10. jadziasman

    jadziasman Prius owner emeritus

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    #10 jadziasman, Sep 4, 2012
  11. jadziasman

    jadziasman Prius owner emeritus

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    #11 jadziasman, Sep 4, 2012
  12. apinson34

    apinson34 Junior Member

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    I figured out the MPG drop guys :) Each of my tires were at 28psi, Which was strange, because the last time I aired them up they were at 40 and 38 in the back, but it did get to cooler temperatures here in GA.

    I did check for a misfire, but there wasn't anything there. After I pumped the tires back up to 40psi, I returned to a 48.6 average! YAY!

    I know the TPMS light would've normally warned me of this, but the sensors need reprogrammed, so currently I don't want to pay $96 to have sensors programmed with a simple tool. Ya know?


    For the battery dying at the start, I think it is definitely the 12 volt battery! This is the next big thing I'm getting for my car, and I plan on getting it within the next week! Thank you PriusCamper for the recommendation!
     
    #12 apinson34, Sep 12, 2012
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  13. PriusCamper

    PriusCamper Senior Member

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    Thank you for thanking me!

    I've been planning on buying a yellow top 12volt battery for a long time, but a poster on here a few days ago pointed out that the quality of that product was much higher before they got bought out and their factory moved to Mexico. People who use to say Yellow top was the best you could buy in the 1990's are changing their tune...

    I still need to do more research in online forums, but Prius users concluding that Yellow Top is superior have little evidence to base that on because the nature of a Prius doesn't put a huge load on a battery when starting up the same way a normal car does. I'll post more once I learn more!

    Are their any Prius Yellow Top owners who have had their battery for 5 or more years? Those are the kinda people I want to here from....
     
    #13 PriusCamper, Sep 12, 2012
  14. John H

    John H Senior Member

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    What needs to be reprogrammed with a tool? I thought you could just reset the TPMS from the vehicle.

    How to Reset TPMs on a Prius | eHow.com
     
    #14 John H, Sep 12, 2012
  15. nh7o

    nh7o Off grid since 1980

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    Or page 155 of the owner's manual.
     
    #15 nh7o, Sep 13, 2012
  16. DanielL

    DanielL Junior Member

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    oops
     
    #16 DanielL, Sep 25, 2012
  17. DumbMike

    DumbMike Active Member

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    Is your wife pulling a fast one on you? Like when you aren't looking, resetting the odometer to zero, then drive the car a little bit so that you don't notice? My girlfriend can be a little devious, too. She thinks I pay too much attention to my car, when the only thing I do is wash it once a month (which is once a month more than my prior car).

    Mike
     
    #17 DumbMike, Oct 1, 2012
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  18. PriusGuy32

    PriusGuy32 Prius Driver Extraordinaire

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    Wife? Girlfriend? The OP is 19! Leave the poor kid alone....lol. Why start scaring him with threatening words like that? :ROFLMAO:

    And for the record, my boyfriend (of 14 1/2 years) knows better than to touch any of my gadgets in my cars or the boat. ;) Not that he drives either anyways but you get the point...
     
    #18 PriusGuy32, Oct 2, 2012
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