P1131 code on 98 Escort | Ford Escort Owners Association (FEOA)

P1131 code on 98 Escort

Discussion in '3rd Gen 1997-2002 2.0L SOHC' started by Dartht33bagger, Nov 18, 2019.

  1. Dartht33bagger

    Dartht33bagger FEOA Member

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    About 2 weeks ago my car set a P1131 indicating an upstream O2 sensor lean condition. I hadn't changed the spark plugs on the car for 60k miles so I bought a new set of plugs, threw them in, cleared the code, and hoped that would be it. On the positive side, the plugs absolutely needed to be replaced because the gaps on two of them were awful. On the negative side, it didn't fix the problem.

    Since the initial SES code, I've had two incidents were the car ran badly. Once at a stop light the car was idling very rough and only picked back up once I gave it some throttle. Another time I was accelerating up a small hill from a stop and at around 20MPH I began to lose power. After about 5 seconds the car picked back up and drove normally. In both these cases, the car was still in open loop and had only been running for 3-4 minutes tops. Other than these two incidents, I don't really feel like the car is running badly. Fuel mileage seems normal, idle is steady, power feels normal.

    Driving home last night my car threw the SES again with P1131. Unfortunately, my scan tool does not have a live data feed, so I can't watch the O2 sensor voltage in real time. All I have the single code and the freeze frame data.

    Code - P1131 Lack of HO2S11 Switches - Sensor Indicates Lean

    Fuel SYS1 - OL-Fault
    Fuel SYS2 - NA
    Calc Load(%) - 45.9
    ECT(*F) - 150.8
    STFT B1(%) - 0.8
    LTFT B1(%) - 0.0
    RPM: 1826
    Veh Speed(MPH): 27

    The fault being in open loop makes me think this has nothing to do the O2 sensor itself since the O2 sensor isn't controlling the fueling in open loop. I've checked for vacuum leaks and didn't find anything or hear anything. What should my next steps be?
  2. marclar

    marclar Moderator Staff Member

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    does it happen when its cold?
    exhaust manifold leaks?
  3. Dartht33bagger

    Dartht33bagger FEOA Member

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    Both times the code has fired its been around 40-45 degrees outside and around the same temperature when I had the idle/power issues. Same for the engine - usually occurs within the first 3-4 minutes of the car running.

    Exhaust manifold leak is interesting. I know at least one of the stud bolts sheared off in the past and is missing. I'll have to take a close look at the manifold gasket tomorrow morning in the light. It sounds like you're expecting this not to be a fuel, MAF or spark issue then?
  4. marclar

    marclar Moderator Staff Member

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    so, a broken stud, and leaking exhaust will cause 'pulses' of cold air to be 'sucked'into the exhaust. when it is cold out you get a 'temp shock' on the sensor. 45* air hitting just after a 1200* exhaust causes the aluminum can inside the sensor that contains the zirconia core to shatter. the reason there is 'no switching' is because the can is shattered, allowing the zircon to short to the case of the sensor grounding it out...
    when the exhust heats up, the gap closes and the sucking in of cold air gets less...
    problem is the sensor is already damaged..

    you need to fix the exhaust leak, and replace the damaged sensor..
  5. rbailin

    rbailin FEOA Member

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    After repairing the damaged head in my last Escort, it soon developed a P1131 problem due to my not thoroughly cleaning the intake manifold of the chemical dip residue from tanking it to clean out the seat remnants. I assume the fumes fouled the sensor. I lived with it for over 2 years.

    During this time, I noticed that the problem of loss of power was only a problem in colder weather, usually within 5 to 15 minutes after startup, usually on long, slight uphill strectches or on uphill ramps or roads. The power loss always resolved itself within 30 seconds or so. I helped it along by shifting into D to reduce the engine load for the duration of the power loss, even at highway speeds.

    The problem might repeat every 30 minutes or so. This is how often the ECU tests the O2 sensor, and the test method generates a too lean condition for a high load in 4th. The test is not run when there's less than 1/4 tank of gas, so it's possible for the code to clear itself simply by it not failing 2 tests in a row, such as when you do several short distance deliveries with stops.

    When the ECU is in open loop due to the code, it relies on a default table of mixtures based on speed and airflow, assuming a default intake temp of say 70°. At colder temps, the air is denser, resulting in a leaner mixture using the defaults, resulting in power loss.

    When I finally replaced the upper O2 sensor, the power loss problem disappeared immediately. If you've never had to change the sensor before this, it may have just worn out from age. Removing a broken exhaust stud may be more of a project than you're willing to take on at this time, especially if the break is below the surface of the head. Simply changing the sensor might be enough to solve your problem for now.
    Last edited: Dec 4, 2019
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  6. marclar

    marclar Moderator Staff Member

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    changing the sensor will be a short term fix without fixing the exhaust leak. same principal of having an exhaust valve brake off from leaking headers..
  7. Dartht33bagger

    Dartht33bagger FEOA Member

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    I'm leaning towards your reasoning rbailin. The exhaust stud has been sheered off since I bought the car in 2011 with 83k miles on it. It seems pretty unlikely that all of a sudden the exhaust manifold would be leaking - but it is possible so I'll look into it just to be sure. I'm hoping its not that since it sounds like a massive project.

    With that said, I have not replaced the O2 sensor on this car, and I'm assuming its still the original sensor. It looks like a new upstream sensor is about $26 on RockAuto. I'd love to confirm that the sensor is truly bad first though. If I bought a usb to OBD2 connector, is there a program that I could use to view thenO2 sensor data in real time?
  8. marclar

    marclar Moderator Staff Member

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    if the stud is gone, its been leaking this whole time.. probably sounds like a tick on startup, then goes away a few sec later.

    as far as your scanner question... ive never used a cheap one like your mentioning.. but if you can get live data, you will see the sensor mv close to 0 volts.
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  9. Dartht33bagger

    Dartht33bagger FEOA Member

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    There is a ticking sound for the first 20 seconds or so after I cold start the car. It then goes away....sigh...it sounds like I may be doing some very major repair work soon.
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  10. marclar

    marclar Moderator Staff Member

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    lol.. there ya go. thats a good start.
  11. rbailin

    rbailin FEOA Member

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    It's only a massive project if the stud is broken off below the surface of the head.

    You can use Forscan at no charge with the correct USB to OBD2 connector. Check out their website for recomendations. My bad sensor was pegged to zero most of the time. When it occasionally produced voltage, hilarity ensued in the form of engine stalling or barely running in heavy highway traffic for up to a minute.

    With emissions parts, I'm partial to using OEM Ford or Motorcraft if they're not overpriced. You can get a DY1401 upstream O2 sensor on Amazon for the same price as good brand-name aftermarket sensors on Rockauto. (The older DY761 sensor is twice as expensive.) I'm not one to throw parts at an engine, but less than $30 is not a big risk. You'll also need to borrow (rent) an O2 sensor socket from your favorite parts store. The short offset style works best in the cramped quarters.
    Last edited: Nov 20, 2019
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  12. marclar

    marclar Moderator Staff Member

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    we only install oem parts here at the shop. we have 2 p1131 fords here right now. can always tell when it gets cold out... the 1131 come out of hibernation
  13. Dartht33bagger

    Dartht33bagger FEOA Member

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    Does anyone know the stud size? I'm going to pick up the parts and fix this in a weekend or two.
  14. rbailin

    rbailin FEOA Member

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    Dorman 03411 Exhaust Manifold Hardware Kit at O'Reilly's or Auto Zone.

    10 M8-1.25 x 56mm double-ended studs and 10 M8-1.25 torque nuts. Use antiseize on both ends.
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  15. Dartht33bagger

    Dartht33bagger FEOA Member

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    Awesome thank you!

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