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Unsolvable Explorer Rough Idle. Any OBD II experts?

Discussion in 'Under the Hood' started by Cashcrazy, October 26, 2016.

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    1. Cashcrazy

      Cashcrazy Active Member

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      2003 Explorer, 4.0 SOHC Flex, 58k. I have been working on my rough idle off and on for about a year. It recently worsened and is driving me crazy. I am not getting any codes and have replaced all the obvious sensors. I recently spent a few hundred on the front end and would really need to properly diagnose what's wrong instead of throwing money at the problem. I started pulling data from the ECM and believe an experienced person in reading it could diagnose this issue. I'm out of ideas and exhausted at this point. The link thread below has everything I have replaced or tested. Anyone seasoned in reading all of the sensor data?

      http://www.explorerforum.com/forums...xplorer-rough-idle.435935/page-4#post-3578465

      [​IMG]
      [​IMG]
      O2 sensor graph below:
      [​IMG]
       
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    3. Stick4503

      Stick4503 Active Member

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    4. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      I suggest monitoring your engine coolant temperature (ECT). Your engine is running slightly rich at cruise and significantly rich at idle. The PCM is compensating by adjusting the long term fuel trims. If your ECT is reasonable then you might try disconnecting the vacuum hose to the fuel pressure damper on the fuel rail and checking for the presence of fuel. Sometimes the damper fails allowing fuel to flow thru it from the fuel rail to the intake manifold. Do your spark plugs indicate the engine has been running rich?
       
    5. Cashcrazy

      Cashcrazy Active Member

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      What is the normal temperature for the ECT? The old spark plugs didn't look bad, but they were worn. I'll pull one this evening and look at a new one.
       
    6. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      When the car sits out over night the ECT at engine start should be a little warmer than the ambient temperature. After engine start is should steadily increase until the thermostat opens at 190 degrees F. After that it should only fluctuate a few degrees above and below 190 while the engine is running. The PCM reads the ECT and adjusts the fuel mixture accordingly. If the ECT sensor is faulty the PCM may assume that the ECT is always colder than actual.
       
    7. Cashcrazy

      Cashcrazy Active Member

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      I'll check it out in about half an hour. I appreciate the response. I am willing to test anything. I'm tired of felling like I am sitting on a riding mower at red lights.
       
    8. Cashcrazy

      Cashcrazy Active Member

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      It appears to be working properly. It ran 192-196 once it was warmed up. Can you think of anything else?
       
    9. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      FPDamper.jpg
       
    10. Cashcrazy

      Cashcrazy Active Member

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      The fuel pressure damper had no fuel seepage. The plugs look great. I've ran these plugs 500-1000 miles.
      [​IMG]
       
    11. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      What percentage of ethanol do you normally fill the tank with? Ethanol is harder on seals than gasoline but since your vehicle is flex fuel rated the seals should be suitable for the fuel.
      There is some reason the fuel mixture is rich which is less common than being lean. Is the engine configuration stock? Have you installed a high flow fuel pump? Have you measured the fuel pressure at the fuel rails? The fuel pressure regulator in the fuel tank could be sticking causing high fuel pressure. Is the main intake hose, filter and inlet clean. Mice have been known to build nests in the intake filter box. Have you cleaned the MAF sensor element with MAF sensor cleaning aerosol? I only drive my Sport about 3,000 miles per year so I add a bottle of Techron fuel injector cleaner to the fuel tank once a year. Since both LTFTs are significantly negative at idle but just a little negative at cruise the amount of excess fuel is probably small and fairly constant. It could be due to leaking fuel injectors but they would have to be leaking about the same on both banks.
       
    12. Cashcrazy

      Cashcrazy Active Member

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      I fill up with regular fuel. The pumps all say "May contain up to 10% ethanol". Everything is 100% stock. Factory fuel pump with a new Motorcraft fuel filter. I have not checked the fuel pressure at the rail. That is one tool I don't have. Main intake hose is clear. The MAF and IAC are new. I have tried multiple bottles of Ethanol treatment, Lucas, STP, Supertech, the whole GUMOUT line, HEET, and Liqui Moly fuel injector cleaner.
       
    13. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      In 2004 Ford switched to pulse width modulation control of the fuel pump to control fuel pressure to reduce emissions. It is possible that late 2003 models may have that also. Check your fuel rail to see if there is a fuel pressure/temperature sensor mounted on the rail (shown below) instead of a fuel pressure damper.
      FuelPressureSensor.jpg
      It has an electrical connector in addition to the vacuum hose connector.
       
    14. Cashcrazy

      Cashcrazy Active Member

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      It has the damper like the first picture
       
    15. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      Which fuel filter does your vehicle have? One type only has two ports - an inlet and outlet.
      FuelFilter.jpg
      The later type has an additional outlet that returns excess fuel back to the tank.
      FuelFilterReturn.jpg
      So far I can't think of another reason (other than high fuel pressure) that might be causing a rich mixture. Your pre-cat O2 sensors are cycling between slightly lean and slightly rich as they should when the PCM is in closed loop. What are their max and min voltages? What are the engine idle speeds for Park with A/C compressor off and on and Drive with foot on brake with A/C compressor off and on? Is the idle rough in Park or just in Drive? There is a brake pedal position switch (BPPS) that lets the PCM know the vehicle is braking so the PCM can unlock the torque converter preventing the engine from stalling. You can easily test the BPPS by engaging cruise control and then tapping the brake pedal to see if cruise control disengages.
       
    16. Cashcrazy

      Cashcrazy Active Member

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      The fuel filter is a Motorcraft FG-1036 which I believe had the port to return excess fuel. The rough idle is the worse in park or neutral. It can be rough in drive but there are times where it becomes acceptable in drive(but never in park). The cruise control disengages fine. I will connect the laptop this evening and get the voltages and the RPM data.
       
    17. Cashcrazy

      Cashcrazy Active Member

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      Could leaky valve covers cause this? I noticed mine leaking a little. It's not dripping but there is a leak. I don't know how much vacuum could be lost there
       
    18. Turdle

      Turdle I bake stuff Staff Member Moderator Elite Explorer

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      what air filter setup do you use? The reason I ask is I see the intake air temp to be 100 degrees. It should be withing a few degrees of outside temperature.

      Do you have an aftermarket filter, or "cold air intake" installed?
       
    19. Turdle

      Turdle I bake stuff Staff Member Moderator Elite Explorer

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      You might check the PCV valve and hose. The PCV vacuum comes from the intake, I do not think a leaky gasket will make any difference. However, leaking PCV hose would allow unmetered air into the system
       
    20. Cashcrazy

      Cashcrazy Active Member

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      Everything is stock on it. The PCV is new and the hose looks ok. It covered one end and blew through it and found no noticeable leaks. It was probably 90 degrees or low 90's when I took that IAT reading. I'll test anything you can think of. I am picking up a fog machine and going to try that this weekend.
       
    21. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      Unfortunately, I am not familiar with flex fuel engines but I looked thru the 2003 wiring diagrams and found that there is a flex fuel sender module in the fuel tank. I assume that the module somehow determines the ethanol content of the fuel which would be needed by the PCM to calculate the desired lambda. The stoichiometric air-fuel ratio of gasoline is 14.7:1 and ethanol is 9:1. With 10% ethanol the stoichiometric AFR would be (14.7 * .9) + (9 * .1) = 13.23 + .9 = 14.13:1 For that fuel the LTFTs should only be about -4%. One of the calibration constants in the tune is the desired lambda. I suspect for a flex fuel engine the PCM calculates a new lambda based on the ethanol content. I don't know if Ford uses wideband O2 sensors for the flex engines but if they don't they should. E85 would have a stoichiometric AFR of (14.7 * .15) + 9 * .85) = 2.2 + 7.65 = 9.85. A standard gasoline O2 sensor would be grossly inaccurate at that value.

      I'm beginning to suspect that your rough idle is not due to the LTFTs. I suggest that you monitor the TPS values with the ignition on but the engine not running. Slowly depress the accelerator pedal and watch for steadily increasing TPS values. Release the pedal and watch that the TPS value returns to the base value indicating the throttle plate is not sticking open. If the TPS values are not erratic then I suggest that you clean the connections to the crankshaft position (CKP) sensor by disconnecting and reconnecting the connector a few times. The CKP sensor is exposed to a harsh environment due to its location. It is critical to the PCM ignition and fuel injection timing calculations. Also, check the connector to the camshaft position (CMP) sensor. It lets the PCM determine if cylinder 1 is on the compression or exhaust stroke.

      Vacuum leaks would result in a lean condition from unmetered air (not measured by the MAF sensor) entering the intake system. Your LTFTs indicate a rich condition which would be normal if using gasoline narrowband sensors with ethanol fuel.
       
    22. Cashcrazy

      Cashcrazy Active Member

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      Thank you. Does anyone know the location of the CKP and CMP? It does sound like these sensors could be the issue.
       
    23. Tech By Trade

      Tech By Trade Well-Known Member

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      Crank sensor is on the harmonic balance, cam sensor is on the top front of the driver side valve cover.
       
    24. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      CKP sensor:
      StrapIt.jpg
      The left red arrow points to the connector.
       
    25. Cashcrazy

      Cashcrazy Active Member

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      Thank you. Crank sensors are cheap so I am going to give it a shot. The sensor on the master cylinder and sensor on the rear differential fully went out. I believe the IAC was also flakey so I do believe these sensors may deteriorate with age. Hopefully I can get it on this evening.
       
    26. Tech By Trade

      Tech By Trade Well-Known Member

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      On a side note, while your looking at that crank sensor, have a real good look at the harmonic balancer. The rubber in it likes to break down and it likes to give way. Could a vibration from a this be causing that sensor to read funny? Just a thought and an easy thing to check.
       

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