Decreased MPG Post Spark Plug and Air Filter Change

Discussion in 'Gen 2 Prius Fuel Economy' started by Nquinto, Jan 2, 2012.

  1. Beachbummm

    Beachbummm Senior Member

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    so, what was the fix?
    if the car was getting over 45 and nothing was changed other then plugs and air filter I don't see how it could be a battery issue...if anything the new plugs should take less energy to fire then worn ones.
     
  2. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

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    It's very unlikely the plug gaps were wrong (unless you dropped them ;o), the manufacturers of these high end plugs caution against trying to adjust the gap, and they're properly set at time of manufacture. I too am wondering a bit about "stp performance filter". Still, I think the smoking gun is the battery.
     
  3. Beachbummm

    Beachbummm Senior Member

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    IDK, I changed my plugs with the same NKG that were in it and I lost about 4 mpg....my 12 volt battery is less then a year old...air filter is the same, just changed the plugs makes no sense to me...the car has more power getting on the highway so I was wondering what the cause is.
     
  4. Mjh3889

    Mjh3889 New Member

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    Still wondering if your problem was fixed? I have the same issue. Lost 10-12 mpg instantly. It makes no sense that people say battery on an instant drop. Even after I put my old plugs back in it didn't go back up.
     
  5. dolj

    dolj Senior Member

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    This an old thread, so you may not get any response from the previous posters.

    If you have a scan tool that can display live data, interrogate the engine coolant temperature sensor while running the ICE from cold. If it doesn't show the temperature rising as it should you will need to check the wiring to it and the sensor itself. If you don't find any fault on the wiring, you will need to replace the sensor.

    Let us know how you got on.
     
  6. Mjh3889

    Mjh3889 New Member

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    My scan tool displays 36 different live figures but I don't think one of them was coolant temp unfortunately.
     
  7. dolj

    dolj Senior Member

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    I find that hard to believe, ECT sensor is one of the most basic sensors.

    Maybe you need to add a PID to your scan tool?
     
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