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Thread: 1500 RPM instability (2012 GT, Edelbrock Blower, LT Headers)

  1. #1

    1500 RPM instability (2012 GT, Edelbrock Blower, LT Headers)

    Hope someone can shed some light on this. I have an "instability" at around 1500 RPM that I can't seem to iron out. Engine runs smoothly at idle and above 2,000 RPM. The trouble spot is between idle and 2,000 RPM, with 1500 RPM being the worst.

    (My log file and tune are at the end of this post)

    Load is constant, spark is steady...but see how the lambda bounces around? (Other RPMs the lambda is steady, and the car runs smoothly).

    Screen Shot 2021-02-08 at 9.12.45 PM.png

    Points of interest:
    1) This only started happening after I added the Edelbrock blower.
    2) It *doesn't* happen for the first couple minutes of run time. It runs smoothly after the engine is started. I suspect that the engine is running in open loop...? (running off cold start maps...?) It's like someone throws a switch after the first minute of driving and then it starts to run poorly between idle and 2,000 RPM.
    3) It runs like a my old carbureted Mustang after I put a single plane intake on it. The engine spit and sputtered below 1800 RPM.
    4) I wonder if this is reversion in the intake manifold that's creating a feedback loop and throwing the mixture off.

    Question:
    1) Any idea how to address this?



    Engine details:
    2012 GT
    Manual Trans
    Edelbrock blower "stage 1"
    LT headers
    Stock MAF
    Stock TB

    Log file:
    Edelbrock 1500RPM instability v43_1.hpl
    Tune file:
    Wes 2012 Mustang GT Edelbrock Blower Headers No Cats v43.hpt

  2. #2
    Advanced Tuner
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    Closed loop fueling is meant to oscillate between rich and lean to keep the catalyst efficient. Try changing 47637 - CL Prop Gain table to reduce the lambda swing.

  3. #3
    Quote Originally Posted by smokeshow View Post
    Closed loop fueling is meant to oscillate between rich and lean to keep the catalyst efficient.
    Yeah, I totally get that. Just that these don't appear to be typical swings. The lambda is swinging in response some strange fueling condition. Lambda doesn't swing like this under any other RPMs or driving conditions.


    Quote Originally Posted by smokeshow View Post
    Try changing 47637 - CL Prop Gain table to reduce the lambda swing.
    That makes sense. I'll try that.

  4. #4
    Quote Originally Posted by smokeshow View Post
    Closed loop fueling is meant to oscillate between rich and lean to keep the catalyst efficient. Try changing 47637 - CL Prop Gain table to reduce the lambda swing.
    By the way, what would be a good starting point for values? Change the values in that load/RPM area to 1.000? More? Less? Here are the OEM values (load/RPM area highlihgted:

    Screen Shot 2021-02-09 at 12.21.24 PM.png

  5. #5
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    When in doubt...go easy. lol

  6. #6
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    Quote Originally Posted by WesDuenkel View Post
    Hope someone can shed some light on this. I have an "instability" at around 1500 RPM that I can't seem to iron out. Engine runs smoothly at idle and above 2,000 RPM. The trouble spot is between idle and 2,000 RPM, with 1500 RPM being the worst.

    (My log file and tune are at the end of this post)

    Load is constant, spark is steady...but see how the lambda bounces around? (Other RPMs the lambda is steady, and the car runs smoothly).

    Screen Shot 2021-02-08 at 9.12.45 PM.png

    Points of interest:
    1) This only started happening after I added the Edelbrock blower.
    2) It *doesn't* happen for the first couple minutes of run time. It runs smoothly after the engine is started. I suspect that the engine is running in open loop...? (running off cold start maps...?) It's like someone throws a switch after the first minute of driving and then it starts to run poorly between idle and 2,000 RPM.
    3) It runs like a my old carbureted Mustang after I put a single plane intake on it. The engine spit and sputtered below 1800 RPM.
    4) I wonder if this is reversion in the intake manifold that's creating a feedback loop and throwing the mixture off.

    Question:
    1) Any idea how to address this?



    Engine details:
    2012 GT
    Manual Trans
    Edelbrock blower "stage 1"
    LT headers
    Stock MAF
    Stock TB

    Log file:
    Edelbrock 1500RPM instability v43_1.hpl
    Tune file:
    Wes 2012 Mustang GT Edelbrock Blower Headers No Cats v43.hpt
    Just curious, dealing with my own E-Force issues.. are you using the Edelbrock calibration that they sent on the SCT X4, or ??
    2016 Chevy SS Sedan M6 SBE LS3, Whipple 2.9L, 3.625 upper/stock lower pulleys for 9.5psi, TSP Stg 3 SC Cam, ID 1050x injectors, LS7 MAF, DSX Aux Pump, DSX Flex Fuel Sensor
    2009 Dodge Challenger SRT8, 6.1 HEMI, Edelbrock E-Force TVS-2300, 9psi

  7. #7
    Advanced Tuner
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    Tyler/Longview, TX area
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    746
    Classic symptoms of a vacuum leak. I had a Shelby do the same thing until I found the leak on the EGR tube. MAF corrections made in the idle region had no effect on the fuel
    trim readings.

  8. #8
    Quote Originally Posted by txcharlie View Post
    Classic symptoms of a vacuum leak. I had a Shelby do the same thing until I found the leak on the EGR tube. MAF corrections made in the idle region had no effect on the fuel
    trim readings.
    That's a solid point. I've noticed at times that the long term fuel trim was adding, like, 25% fuel at idle and I chalked it up to something I'll have to figure out later." That would also explain a nasty off-idle nosedive I'm getting too. I'll do some investigation and see if I can find the any leaks and report back.

  9. #9
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    Just remember a vacuum leak can be anywhere from the MAF sensor to the intake valve or from the exhaust valve the O2.

  10. #10
    Quote Originally Posted by txcharlie View Post
    Just remember a vacuum leak can be anywhere from the MAF sensor to the intake valve or from the exhaust valve the O2.
    I was unable to locate any vacuum leaks.

    Is this a possible O2 heat or transport delay issue? Is there a way to keep the O2 heaters on, or is that even "a thing" with wide band sensors? (Note that tune is attached in OP for reference).
    Last edited by WesDuenkel; 02-17-2021 at 11:04 AM.

  11. #11
    Advanced Tuner
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    Mar 2018
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    447
    Have you fixed your injector data? You have ford's data and when I used that on my car it ran like crap.

    Look in my LU47 thread and use txcharlies data from the tune he posted.

  12. #12
    Quote Originally Posted by K44 View Post
    Have you fixed your injector data? You have ford's data and when I used that on my car it ran like crap.

    Look in my LU47 thread and use txcharlies data from the tune he posted.
    Huh, OK. I'll give that a shot and report back!