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P0171 and my 2001 Focus

Discussion in 'Ford Focus' started by 7lrh11, Feb 9, 2018.

  1. 7lrh11

    7lrh11 New Member

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    My 2001 Focus 2.0l SOHC split port threw a check engine code P0171 2 weeks after I bought it. I found 2 hoses that had to be replaced and done so. The one coming off the PCV valve was collapsed. The other was split. I also changed the PCV valve. I cleared the code thinking this had to be the cause. 3 days later the light returned. I do have a scan tool. The STFT and the LTFT are real high. 32 positive for the Long term, and around 22 for Short term. When I do increase the RPM's up to 2500, the trims are normal on Live Data. There is no issue with how the car runs. It's a peppy little thing. My question is can this be a sensor issue, or vacuum leak, or anything else. I do believe that it is burning more gas then it should be. While watching the scan tool on the o2 sensors, I noticed that the #1 sensor had what I think is a normal up and down pattern. And the #2 sensor is showing pretty much a flat line. Am I understanding that maybe #2 needs to be replaced? Sure need help!
  2. Action

    Action Moderator Staff Member Respected Member

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    After you did the repairs (hose replacements) and cleared the code, did the same code come back when the CEL came on? (You didn't state)
    If this code did come back it is stating the fuel injection system is too lean.

    Replace air filter if not new.
    Vacuum leaks would be common.
    Crank case vent system leaks. (Are your hoses fully connected & connections tight)
    Mass air flow sensor - and that may need cleaning
    Front O2 sensor - not rear for this code. The rear is looking at Cat C. efficiency.

    With less than 100,000 miles it would be a bit early for O2 sensors to be replaced.

    >>>>>>>>>>>Action
  3. Action

    Action Moderator Staff Member Respected Member

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    "The STFT and the LTFT are real high. 32 positive for the Long term, and around 22 for Short term. When I do increase the RPM's up to 2500, the trims are normal on Live Data."

    Sounds like the system is compensating for a lean condition. It pumps in more fuel to offset the lean condition. This is to make a total burn of the fuel charge. Getting that signal from the front O2 sensor. At higher RPM the system is pumping more fuel anyway and the system may not be as lean. (because of a vacuum leak or a leak down stream from the throttle body) So the fuel trim pulls back and the vehicle is running leaner because it does not need the fuel trim at the higher RPMs.

    The highest vacuum would be at idle. As the throttle body is opened up there is normally less of a vacuum signal so a vacuum leak has less impact at higher RPM.

    >>>>>>>>>>Action
  4. redrag

    redrag Active Member

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    i'ld say your long term trim is high because of the leaks you fixed. check again tommorow and i bet it will be lower. like action said , look for more leaks
  5. redrag

    redrag Active Member

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    o2 #2 downstream. better be smooth compared to upstream, otherwise your cat is bad
  6. 7lrh11

    7lrh11 New Member

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    Thanks for the responses. Yes the same code did return, so I didn't fix it. I did fail to mention that I did clean the Mass Air Flow sensor. All the new connections made with the new hoses are good and tight. Tomorrow I will be going to the mechanics shop, for he is going to help me find if there is a vacuum leak. And thanks for the info on the O2 sensors. I also failed to say that the leaks I fixed were done last week. And yesterday is when I checked the fuel trims. Those readings are what the engine is experiencing currently.
    Thanks again focus forum!
  7. Action

    Action Moderator Staff Member Respected Member

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    Post back on what you find out.

    >>>>>>>>>>>>Action

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