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Thread: P0174 Too Lean, Crankshaft Position Sensor CKP?

  1. #1

    Default P0174 Too Lean, Crankshaft Position Sensor CKP?

    So I've been battling a rough idle problem and have the following question:

    Is it possible for a faulty CKP to cause the engine to throw a too lean condition code?

    I was actually expecting it to throw a too rich code because when I checked for spark I did not get spark every time I tried to start the vehicle, and other than the obvious relays, battery, and fuses the most common reasons for no spark on this vehicle would be the crankshaft or camshaft position sensor or the PCM...

  2. #2
    Registered oldgeezer's Avatar
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    P0174 = System too Lean (Bank 2)

    It would really be helpful if you gave more info on what you are driving. The "Bank 2" probably means a WJ. On the 4.7 engine it is the passenger side cylinder bank. On the 4.0, it is the front three cylinders. Your problem is most likely a failing upstream (engine side of the cat converter) O2 sensor in the Bank 2 exhaust.

    The primary purposes of the CKP are proper ignition timing and misfire detection. It is not likely it has anything to do with your trouble code.

    No spark could mean a faulty CKP, but in that event the code would be P0320. No spark could also mean a bad ASD relay or a blown ASD fuse.
    2001 WJ Limited, 4.7L, Quadra-Drive -- Kenne Bell Supercharger, Stillen Rotors with MM pads (F/R), Addcos (F/R), Kolak 3 inch exhaust with large case MagnaFlow, Rogue Chrome wheels, DRL activated, and Blaupunkt 3.5" dash speakers.

  3. #3

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    It's a 4.7L

    The thing is, she runs rough, it's my understanding that the o2 sensor isn't used at startup so I've at least partially ruled that out.

    I also understand that when the CKP fails it doesn't always throw a code.

    I've swapped the relays and checked all fuses.

    So if there is a problem with the CKP, could it cause a rough idle?

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    Quote Originally Posted by Briandl View Post
    It's a 4.7L

    The thing is, she runs rough, it's my understanding that the o2 sensor isn't used at startup so I've at least partially ruled that out.

    I also understand that when the CKP fails it doesn't always throw a code.

    I've swapped the relays and checked all fuses.

    So if there is a problem with the CKP, could it cause a rough idle?
    The O2 sensor is for the P0174 code, but a lean enough condition could lead to rough running due to occasional misfires when the lean mixture fails to ignite or burn properly. It's true that the O2 sensor does not affect start up.

    Earlier, were you saying that it is hard starting? And while the starter is cranking, you don't always get a spark, but do get one eventually and it starts?

    Your are correct that a problematic CKP doesn't always throw a code.

    Yes, a problem with the CKP could easily cause a rough idle and would probably cause rough running, especially while accelerating quickly. It would also cause hard starting.

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    The thought occurs to me that nothing is wrong with the O2 sensor and the message is accurate. That is, the mixture is truly lean and that means a fuel supply problem. However, i can't think of a way that one bank would be lean without the other side being lean as well.

  6. #6

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    Quote Originally Posted by oldgeezer View Post
    The thought occurs to me that nothing is wrong with the O2 sensor and the message is accurate. That is, the mixture is truly lean and that means a fuel supply problem. However, i can't think of a way that one bank would be lean without the other side being lean as well.
    That's what I was thinking.

    I actually expected it to either throw a CKP sensor error or a too rich error because I wasn't getting good spark.

    If the CKP can't cause it to run lean, then I may very well have a fuel supply problem.

    The only thing I've noticed is that when I push the tab on the fuel pressure test port, a little fluid comes out, but not a lot, it squirts up maybe an inch for a second and that's it, I was really expecting a spray.

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    Get a pressure gauge on it to check the pressure from the pump to the rails. It should be more like a geyser when you push the test port valve down. The fuel pressure should be in the 50psi area. If it is low it could either be a bad fuel pump or the fuel pressure regulator that is part of the fuel filter has gone bad.
    99 WJ (yeah, the wife took it)
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  8. #8

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    My book says between 44.2-54.2 at idle, problem is I can't get her to start.

    I hate to just throw money at the problem but if I send it to someone it's going to cost me more than if I just try replacing the CKP, especially since it will have to be towed someplace.

    And regardless of fuel pressure, I'm still not getting a spark and my book says if I don't it's either the CKP, CPS, or PCM.

    I've checked the connector to the spark plug coil for voltage, and checked the coil itself for resistance, it all checks out, but I don't get spark and a test light doesn't blink when I try to start the Jeep...

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    Any luck? I am having the same problem with the same code.
    HEMI LTD

  10. #10

    Default Soot in the tailpipe

    Same problem here, however I noticed that the tailpipe is loaded with carbon soot, and on the garage floor as well. Would an excessively lean mixture on Bank 2 cause a carbon soot excess?

  11. #11
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    Somebody with P0174 should measure, or have someone else measure, the pressure at the fuel rail when the engine is warm and running and post the results. That would confirm whether or not enough fuel is getting to the engine.
    2001 WJ Limited, 4.7L, Quadra-Drive -- Kenne Bell Supercharger, Stillen Rotors with MM pads (F/R), Addcos (F/R), Kolak 3 inch exhaust with large case MagnaFlow, Rogue Chrome wheels, DRL activated, and Blaupunkt 3.5" dash speakers.

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