Running lean P0171

Discussion in 'Gen 3 Prius Technical Discussion' started by Jonny Morrow, Jun 11, 2021 at 2:02 AM.

  1. Jonny Morrow

    Jonny Morrow Junior Member

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    Hey friends,

    My 2010 just threw a P0171. I’m getting crap gas mileage and the engine does seem pretty weak. I’m thinking probably fuel delivery. Any tips? How is the fuel pump powered? The 12v battery or the traction battery? Could my 12v battery be low?

    Thanks!
     
  2. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Miles?
    Service history?

     
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  3. Jonny Morrow

    Jonny Morrow Junior Member

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    160,000. No service history other than oil changes and a water pump a few years back. The car is well cared for.
     
  4. Grit

    Grit Senior Member

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    well cared w/o either coolant changed? o_O
     
  5. Jonny Morrow

    Jonny Morrow Junior Member

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    Looking for suggestions related to fuel delivery please…
     
  6. Samuel Williams Jr

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    Tech stream is cool, but if the Prius has a Schrader on the fuel rail? You can rent a fuel rail test kit to check it.

    Do the 02 sensor's test good? That/those would be my other guess.
     
    #6 Samuel Williams Jr, Jun 11, 2021 at 6:00 PM
    Last edited: Jun 11, 2021 at 6:50 PM
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  7. Mdv55

    Mdv55 Active Member

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    It's not always fuel delivery.......excess air can cause a lean condition too.

    In my case, I reused the intake manifold gasket when I put it back together and had to go back in and replace it a few thousand miles later.

    If you really think fuel, maybe an injector cleaner is a cheap way to start. Check all hoses after the MAF and make sure there aren't any unmetered leaks presents. Have you cleaned the MAF yet?

    If you don't have a proper way to diag anything keep it simple and start with the easiest things first.

    Can you monitor fuel trims? See what the 02 sensors are doing? That will give you more insight.

    If you're focused on the 12v do you know what the resting voltage is? How old it is?
     
  8. Jonny Morrow

    Jonny Morrow Junior Member

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    Thanks for the great replies guys.

    My MAF looks brand new inside and out and visually all hoses are in excellent shape. No obvious leaking.

    I’m gonna check fuel pressure next and report back. At least discovering fuel pressure will help me rule that out or not.

    Anyone here know if a 2010 has a Schrader valve and where it is?
     
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  9. ChapmanF

    ChapmanF Senior Member

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    It doesn't. Even at a dealership they'll just unhook the hose at the firewall and MacGyver something up with a tee and fittings. They have part numbers if you want to do the same 'official' MacGyverage that they would.

    gyver.png
     
  10. Samuel Williams Jr

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    Sigh, well that is an annoying PIA! But I have a few Plan B's! :)

    Pull the fuel rail put a paper or rag down and see if the injectors spray as you crank it over? That won't tell if you the fuel rail pressure is enough but it's a start.

    You could also say, just screw it and replace the fuel pump anyway? E bay or a local Pick and Pull, would work for that approach. Fuel pump failures do seem to be rare in Prii so most likely a used one would be fine?

    Or if you are into buying tools. anyway? Most likely this kit.:
    JIFETOR Fuel Injection Pump Pressure Tester Gauge Kit, Car Gasoline Gas Fuel Oil Injector Test Manometer Tool Set 0-140PSI, Universal for Auto Truck SUV Motorcycle ATV RV SUV
    Hmm I can't post a direct link to Amazon but that is the kit I saw. to test it?

    But that kit and ChapmanF's post should set you up to test the FP, yourself?
     
    #10 Samuel Williams Jr, Jun 13, 2021 at 5:56 PM
    Last edited: Jun 13, 2021 at 6:02 PM
  11. ChapmanF

    ChapmanF Senior Member

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    Well, if the engine is already running, but just running lean, then some fuel is already coming out the injectors. I don't think you would learn very much useful from only seeing that, unless you could also measure the rail pressure or have the injectors tested on a flow bench.
     
  12. Samuel Williams Jr

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    Yeah I have to agree. I was trying. :)

    I'd just replace the pump (anyway) and move forward ... sometimes, "Wack A Mole Works." :)
     
  13. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Are you the original owner?
    If not, why do you presume that the car has been well cared for absenting maintenance records for all of the things that are required in 11 years and 160,000 miles of service besides.......oil changes?

    Two things can be true at once.
    It is possible that maintenance has been performed on this car that has not been documented - AND - the car has been "well cared for."
    HOWEVER (Comma!) generally speaking, people that are anal about car maintenance are also pretty reliable for writing things down.

    A car that has only had oil changes for the last 160,000 miles is *NOT*....."well cared for."
    Has this car exibited the "Prius Death Rattle" ........YET?

    https://www.toyota.com/t3Portal/document/omms-s/T-MMS-10Prius/pdf/2010_Prius_WMG_0W20_lr.pdf
     
    #13 ETC(SS), Jun 14, 2021 at 1:06 PM
    Last edited: Jun 14, 2021 at 1:12 PM
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  14. Jonny Morrow

    Jonny Morrow Junior Member

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    Ok, For the folks in the thread who keep bringing up scheduled maintainance let’s go ahead and say the car has never been maintained. Ever. No oil changes, no fluids, no wipers, no tires, no bulbs. Nothing. But amazingly the only issue I’m having is a lean condition.

    For those who have made suggestions, I appreciate it. Going on a mission for the tube connector I need to finish my fuel pressure test. Thanks for the great post ChapmanF. I’ll report back on fuel pressure soon. Anyone know what the normal pressure range is?
     
  15. mr_guy_mann

    mr_guy_mann Active Member

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    44-50 psi. If you can do so safely, then test pressure with the engine under load (sometimes I tape the gauge to windshield and go on a test drive). While a bad pump can (once in a while) cause low fuel pressure all the time, the more common failure is to have adequate operation at low engine speed and load, then pressure drops under higher load and demand (along with a loss of performance).

    Do you know what fuel trims are doing under different conditions? Might help point a finger in the correct direction. Example, a vacuum leak will cause high trim only at idle- at higher load and rpm trims will be very close to normal.
     
    #15 mr_guy_mann, Jun 15, 2021 at 11:36 PM
    Last edited: Jun 15, 2021 at 11:42 PM
  16. Jonny Morrow

    Jonny Morrow Junior Member

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    28 psi is the best I could get both idle and hard accel. Fuel pump in the mail. I’ll report back. Thanks all!
     
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