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Thread: Revving past 8000+ rpms

  1. #21
    Lifetime Member Bruce Melton's Avatar
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    Rob,

    Not to raise your anxiety, but when you lose fuel abruptly at those rpms under load it is putting a helluva load on the mechanical parts such as timing chain and rotating parts. All those high buzzing parts are trying to go to zero almost instantaneously.
    Gives me the chills.

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  2. #22
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    Quote Originally Posted by Bruce Melton View Post
    Rob,

    Not to raise your anxiety, but when you lose fuel abruptly at those rpms under load it is putting a helluva load on the mechanical parts such as timing chain and rotating parts. All those high buzzing parts are trying to go to zero almost instantaneously.
    Gives me the chills.
    I hear ya Bruce.
    If I'm quick enough, I'm into the shift already and it doesn't rock the car much at all.
    Once we know the point of cutoff we can set the limiter 50 rpms before it and also I can adjust my shiftlight to avoid activating any cut off.
    With the knowlegde I will be prepared and be able to protect the car.
    That's why I'm so determined to figure out how to get past the hurdle or work around it.
    I really don't want to go to an aftermarket computer.

  3. #23
    Joe (Moderator) joecar's Avatar
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    Update on the other thread, see post #204: showthread.php?t=11706

  4. #24
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    Quote Originally Posted by joecar View Post
    Update on the other thread, see post #204: showthread.php?t=11706
    Joe I have no issues/symptoms similar to his, so I don't believe anything is mechanically broken.
    I do however feel that maybe the signal is not being picked up clearly @ high rpms.

    That doesn't explain the fuel cutoff to me but maybe why it cuts off at different rpms.

  5. #25
    Joe (Moderator) joecar's Avatar
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    If you can get access to an oscilloscope and get waveforms for CKP and CMP at various RPM's 2000, 4000, 6000, 7000, 8000, 8000+...

    then we could compare the sets of waveforms... this will show if the signal integrity is failing at high RPM...

    without an oscilloscope there's no other way to know.

  6. #26
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    Quote Originally Posted by joecar View Post
    If you can get access to an oscilloscope and get waveforms for CKP and CMP at various RPM's 2000, 4000, 6000, 7000, 8000, 8000+...

    then we could compare the sets of waveforms... this will show if the signal integrity is failing at high RPM...

    without an oscilloscope there's no other way to know.
    Be careful because the presence of the O-scope in the PCM harness' circuit may be enough to change the behavior. You may actually artificially decrease the signal integrity by adding some other device to the loop.

    If you could put the CAM/CKP sensors on a separate rig with their target wheels and verify the waveforms outside of the vehicle, it would be a more scientific test. Cumbersome, but more reliable.

    So, the real issue remains that somewhere between the CAM, CKP, and PCM there's just not a reliable enough signal beyond 8000rpm. I saw this on another PCM at a previous employer, and the only solution was to create an ENTIRELY NEW PCM that was capable of working with speeds that high.
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  7. #27
    Joe (Moderator) joecar's Avatar
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    Using a x20 (typically 20+MΩ impedance) attenuator probe and keeping the ground isolated should be ok, that won't modify the signal.

    But, just using a x1 probe (~1MΩ) will modify the signal.

  8. #28
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    Quote Originally Posted by I saw this on another PCM at a previous employer, and the only solution was to create an [I
    ENTIRELY NEW PCM[/I] that was capable of working with speeds that high.
    Hi Greg. If there is any way it can be done, or anyone you can refer me to to do this I would go for it, as I am officially "PCM limited" on the drag strip.

    I cannot shift higher than ~8000 rpms and now I'm hitting this HARD limit before the stripe in 4th. A double wammy.

    Who can reprogram a completely new PCM?

    I've been told it has been done but have never seen any evidence and apparently everyones's too busy to do the job. Not sure if someone's just blowing smoke up my a$$.

  9. #29
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    Quote Originally Posted by robz View Post
    Hi Greg. If there is any way it can be done, or anyone you can refer me to to do this I would go for it, as I am officially "PCM limited" on the drag strip.

    I cannot shift higher than ~8000 rpms and now I'm hitting this HARD limit before the stripe in 4th. A double wammy.

    Who can reprogram a completely new PCM?

    I've been told it has been done but have never seen any evidence and apparently everyones's too busy to do the job. Not sure if someone's just blowing smoke up my a$$.
    Greg doesnt mean simply reprogramming a new PCM, anyone can do that with a Tech II or if EFILive supports full flashing of said PCM. I believe Greg's solution was to go back to the drawing board and actually make a brand new physically PCM that would have better control over 8000rpms. Basically, its impossible to do without the resources of a major automaker.

    Have you thought about switching to a standalone to control fueling/spark above 8000rpms?
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    Quote Originally Posted by ScarabEpic22 View Post
    Greg doesnt mean simply reprogramming a new PCM, anyone can do that with a Tech II or if EFILive supports full flashing of said PCM. I believe Greg's solution was to go back to the drawing board and actually make a brand new physically PCM that would have better control over 8000rpms. Basically, its impossible to do without the resources of a major automaker.

    Have you thought about switching to a standalone to control fueling/spark above 8000rpms?
    Yes. I have thought about it. I want to maintain factory gauges, however.
    I'm surprised no one has figure out a way around this, but I'm sure ther'e just not enough people interested.

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