Fuel economy decrease after replacing fuel pump

Discussion in 'Gen 3 Prius Fuel Economy' started by newguywithpups, Nov 23, 2021 at 9:38 PM.

  1. newguywithpups

    newguywithpups Junior Member

    Joined:
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    Location:
    Seattle(ish), WA
    Vehicle:
    2011 Prius
    Model:
    N/A
    When I bought my Prius used a couple years ago it had a P0171 "system too lean" error.

    Over the past couple years I tried different fixes that had no effect - replacing MAF sensor, changing spark plugs and fuel injectors. They also didn't seem to affect the fuel economy, which hovered around 46mpg as measured by the amount driven (odometer) / amount of fuel refilled.

    A couple months ago I tried exchanging the fuel pump with a used one from eBay - immediately my LTFT dropped from ~+30% to around 0, and since then the check engine light hasn't come back on, which all seems to indicate the original P0171 error is fixed.

    However, exactly after the fuel pump replacement, my fuel economy has sunk to around 42mpg.

    From other threads where people fixed their P0171 by replacing the fuel pump, they reported significant increases in fuel economy, so I was expecting the same.

    Any ideas what the issue might be? Maybe I should've just kept the error. I don't have smog checks in my state anyway. :( It's like I paid all this money to troubleshoot and make the error go away, only to effectively decrease my fuel economy and nothing more...
     
  2. ASRDogman

    ASRDogman Senior Member

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    Perhaps the "used" is weak and not able to get the pressure up where it should be.
     
  3. douglasjre

    douglasjre Active Member

    Joined:
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    Location:
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    Vehicle:
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    ----USA----
    You probably have a small evap leak that will show up after a couple more drive cycles. If it does you'll have to put some silicone grease on the seal
     
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