Nock senser location

Discussion in 'V8 - Maintenance & Troubleshooting' started by patrick hubbard, Aug 19, 2019.

  1. patrick hubbard

    patrick hubbard Member

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    I think my nock senser whent out. My ecm isn't pulling timing or giving it any it's staying at 0 degrees
     
  2. NoSlo

    NoSlo GoldMember

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    The knock sensor is located under the intake and fuel rails, adjacent to the PCV crankcase cover plate.

    The sensor is, to the best of my recollection and inference, a piezo contact microphone, actually listening for the octane knock, and will compensate for octane accordingly under current conditions. No output is interpreted as no knocking, the only failure mode I could imagine.

    Pulling the "spout" connector will set timing constant.
    ----

    Edit: Didn't see this was G3 with sleepy eyes. G3 has two knock sensors - under the intake, there's one on either side of the PCV plate at the center of the engine.

    How and why are you checking timing? To get actual timing, you have to acquire the falling edge, the off signal, of the coil signal wire, not something your average clamp-on timing light would do.


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    More V8 info

    Failure Mode Effect Management

    During some electronic ignition system faults, the failure mode effects management portion of the PCM will maintain vehicle operation:
    - If the spark output signal is interrupted, the PCM will turn the ignition coils on and off using the crank sensor signal. This will result in fixed spark timing (10 degrees BTDC) and fixed dwell time (no CCD).

    ...

    The PCM uses information from the cam position sensor to generate an internal PIP (profile ignition pickup) signal. Once the PIP signal is generated, fuel and spark are enabled (otherwise random-start fallback mode). The calculated spark target is used internally by the PCM as a PWM digital signal called SPOUT (spark output). The PCM decodes the SPOUT signal and fires the next spark at the commanded spark target. The PIP signal is also used to for the tachometer.

    So - basically no cam signal or no computed "spout" from that, and it is in fallback mode. There is also the "octane adjust shorting bar" with unclear function. That is, if you are actually testing correctly.

    [​IMG]
     
    Last edited: Aug 19, 2019
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  3. patrick hubbard

    patrick hubbard Member

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    Where can I buy new knock sencers and repair harness
     
  4. NoSlo

    NoSlo GoldMember

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    I think you are asking the wrong questions.

    An example of a good question: Does your car reliably start every time, or does it take several tries?

    It may be be good to take a step back, and share the symptoms you are experiencing, and what lead you to start checking the non-adjustable ignition timing. Then we might discover if you are completely barking up the wrong tree, or are performing the (non-existant) procedure incorrectly.

    There are two sensors, each with its own PCM connection. If one failed, the other would continue functioning, detecting pre-ignition from low octane fuel and making trim corrections. The symptom of them not working would be engine pinging on cheap gas.
     
  5. patrick hubbard

    patrick hubbard Member

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    I use 91 octain. My car doesn't start easily. And the other day I tried to take it past 120 and it would not never hit a speed limiter. I hooked up the scanner at work checked for codes and found one and I can't remember the number but it said knock senser circuit malfunction. So I went into engine data and looked to see what my timeing was doing and it was 0 degrees to 1 degree
     
  6. patrick hubbard

    patrick hubbard Member

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    Also have only 30 pounds of fuel pressure. Yet it seems to smell like it is running rich.
     
  7. gamefanatic

    gamefanatic SHO Member

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    And no leaks in the regulator?
     
  8. patrick hubbard

    patrick hubbard Member

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  9. gamefanatic

    gamefanatic SHO Member

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    Have you checked the fuel injectors to see if they are leaking?
     
  10. patrick hubbard

    patrick hubbard Member

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  11. NoSlo

    NoSlo GoldMember

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    The reason why I ask the question about starting - if the crankshaft sensor is failing, you will only start on one out of four tries, no matter how long you crank. That would also cause the vehicle to revert to base timing, running OK but underperforming.
     
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  12. luigisho

    luigisho SHO Member

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    As far as knock sensor question, I saw some on rock auto and I am not sure about the wiring. I thought I saw some on an internet site but they were listed for sable and maybe taurus and not sure if they crossed over to the 3.4
     
  13. GEN 3 SHO FAN

    GEN 3 SHO FAN SHO Member

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    30 psi of gas pressure is ok at idle (40 psi under max load). This coming from the Ford blus book SHO supplement. (According to some olds posts, they are running rich from factory.)

    (If the code isn't really precise, the crank sensor is around 5$ and camshaft sensor is also around 5$. Tightened by one bolt each. It simpler to try these before going to the knock sensors.)
     

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