p0171 p0174 diagnosis symptoms troubleshoot lean condition

Discussion in '2005+ Mustang GT 4.6L Tech' started by Mustangk, Jan 10, 2021.

  1. Mustangk

    Mustangk Junior Member

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    • cant get rid of p0171 and p0174 had some other issues that led to replacing tb and pretty much a fresh primary and secondary ignition components overhaul.
    • Sct noticed tunes stacked ontop of each other possibly causing issues
    • I got Ford to reflash pcm to stock.

    1. after battery reset car runs fine with no cel and then on first engine off and engine start it'll pop cel and p0171 p0174 and a clutch pedal position circuit a or b code althoug ivthink clutch pedal code is a problem I've had for a while and separate.
     
  2. 07 Boss

    07 Boss Senior Member

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    Without any more info, all I can say is you don't have enough fuel or you have too much air. Could be bad injectors, fuel pressure, filter, tune, vacuum leak, exhaust leak....
     
  3. Mustangk

    Mustangk Junior Member

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    yah i cant even imagine what info i could share that would be relevant since the code is so broad and all so relative to many bits of information being correct. for example, i have new 3 month old injectors, brand new tb, fuel pressure holds at 40 to 43 when i key on engine off and cycle key, runs at 48.3 or 49.3 whichever is the proper fp so pump seems fine.. pressure jumps to like say 45 or so when u get on it whivh seems normal and then quickly returns to around 48.3, no tune since i got the pcm reflashe to stock as i was having no start issues a month ago, i cant find an obvious vac leak, tightened down all the intake manifold and tb has no air leaks, using stock air box with no leaks, maf sensor isnt leaking and is also brand new, exhaust may have a leak but ive tightened the cat to midpipe flange probably once every 2 to 3 weeks that if i tighten it again i feel like ill snap it although it could be off center and not seating correctly, but in regards to the exhaust connection isnt it post the first o2 sensors so the lean condition wouldnt read the sensor
     
  4. 07 Boss

    07 Boss Senior Member

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    I'm assuming the 3 mos old injectors are oem replacements, stock size? The fuel pressure kinda has me baffled. It should change relative to manifold pressure or vacuum. Meaning at idle it should be less than what it is with the key on and engine off. If I am wrong, someone correct me. When you step on the gas the manifold vacuum decreases and the fuel pressure should go up. But I think this would cause a rich issue. Maybe she is running rich and the ecu is overcompensating. IDK, but the pressure thing bothers me. The exhaust leak would not effect the upstream sensor unless the leak was pretty close. I forgot where the stock sensors were as mine are down under the car in the mid-pipe. I will tell you another little story though as I was occasionally getting a lean code and couldn't figure it out until I swapped in the actual original equipment sensors. Just seemed like the other brands like bosch or whatever were sketchy. I replace all four sensors with the original equipment as opposed to the replacement parts ford sell or tells you to get and have not had that code pop up in about a year. Or until I had an actual exhaust leak. Not saying that is your issue but bad sensors are a possibility. Do you have the capability of data logging?
     
  5. Juice

    Juice forum member

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    You need to look at live pcm data. As you said, such a broad code, the actual fault code may be just pending and has not matured yet to trip a code,
    So, you need someway to look at what the Upstream O2 sensors doing, short trem fuel trim, water and air temp sensors, and maf reading, etc.
    I use Torque app on my phone or Forscan on a laptop to view live data. Have to see what the pcm is doing.
     
  6. Mustangk

    Mustangk Junior Member

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    is there a list that explains the significance of each data point, for example: whats maf reading mean and whats its supposed to be, whats tp sensor voltage mean and whats right and whats broken, whats fuel pump voltage supposed to be and whats it mean,
     
  7. Juice

    Juice forum member

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    Not to my knowledge.

    Basically what trips those codes is that the PCM sees nothing wrong hardware wise, and the O2 sensors are asking for more fuel. So the PCM trips the lean codes, the actual AFR is not what is expected.

    Had something similiar happen to me on a daily driver. Every week, right on schedule, the lean codes would trip. No running issues. I couldn't find anything that would cause it. So I replaced the intake manifold (tsb recall that was never done) and the lean code never came back. I had a vacuum leak between the heads and intake manifold. (4.6 2v) A tiny vacuum leak is almost always the root cause of lean codes on a car that otherwise runs fine.
     
  8. Mustangk

    Mustangk Junior Member

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    i think i found it, found one of the corner bolts to header was like a full turn loose. Tightened it up and the exhaust note sounds cleaner and it runs a alot better almost like new again also after pcm reset no codes
     
  9. Mustangk

    Mustangk Junior Member

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    does this run true if the stat i was referring to as "fuel pressure" was really "fuel pressure drop across injectors" one of the data points available on SCTx4. it seems to hover strong around 39 or 38 psi
     
  10. 07 Boss

    07 Boss Senior Member

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    That may be that it is reading relative pressure and then that is fine. Your car will command 39 psi over manifold vacuum or pressure. When I go into boost my actual pressure is like 50+ psi but relative pressure stays at 39 psi.
     
  11. Mustangk

    Mustangk Junior Member

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    weird i had it disappear found loose exhaust manifold from a power steering leak splashing onto the nuts, tightened it up and for a week or 2 it didnt pop 171 or 174. but now had it again. putting on some jba shorties as we speak and will see what happens, does nayone know if jba shorties require a tune
     
  12. Juice

    Juice forum member

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    Shorties do not need a tune.
     
  13. Mustangk

    Mustangk Junior Member

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    its a good day today then.! in the proceess of tightening up some new jba's and lowering the car back off jack stands, i hear i may have to pull the motor towards passenger side to have enough clearance from frame rails and steering shaft, as well as may need to buy adjustable prothane mounts to lift the engine for clearance from frame rail and steer shaft. Anyone have any directions on how to "pull/pry" the engine and tighten mounts, or if the engine is supposed to be lifted or lowered with the adjustable prothane mounts, as they seem to come with big thick "1/4?" washers that are used to determine the height of change. So im wondering if hypothetically if you use no washers it would be "3/4" lowered, that is using just the prothane mount, and if you used all 3 it would be raised "3/4" of an inch. if researched correctly, i think i need to raise engine
     
  14. Dino Dino Bambino

    Dino Dino Bambino I have a red car

    Age:
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    You'll need to raise the engine to install the headers but they're supposed to have just enough clearance to allow you to reuse the stock mounts.
    Let us know how it goes. I still have a pair of JBA shorties in a box that I haven't installed yet so I'm interested to hear if you have any issues before I do mine.
     
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