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Thread: Offset Voltage Question

  1. #1
    Tuner seven ends's Avatar
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    Offset Voltage Question

    Groiunded and regrounded. Currently have a 12 guage from WB analog ground wire back to battery negative post. Have taken two 14 guage grounds back from MPVI interface EIO (ports 5 and 6) to same battery negative post.

    This is my best voltage readings so far with the additional grounding at Free Air CAL- on my AFX:

    WB analog signal = 4.96 V (confirmed by two meters)
    HPT Voltage Histogram = 4.8127 V

    Does this alone warrant an offset adjustment?

    If so, do I offset 4.96 back to 5 V?

    Or do I offset 4.8127 V back to 4.96 V?

    Or do I offset 4.8127 V back to 5 V?
    2010 Avalanche 4WD; AES 390; Mast LS3 heads; VVT Cam; ported TVS2300; Overdrive 8 rib pulleys; 2.7 snout pulley; ID1000; LS3 TB; WB 450; Twin MM cans; built 6L80; CircleD Triple Disk, CSR flexplate; Trucool 40K; Aeroforce Dual; AFX

  2. #2
    Advanced Tuner Pulse_GTO's Avatar
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    What wideband are you using?

  3. #3
    Tuner seven ends's Avatar
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    I was using the PLX-300 previously. I was simulating the NB then. It normally read lean resulting in a slightly richer tune. However, good enough not being good enough I purchased an AFX, removed PLX, added a bung, put both NB's back, and have been spending more time grounding, super-grounding, calibrating, offsetting, and am slowly tune by tune with the AFX getting back to the last one I did with the PLX. Hey practice makes perfect and warming up to FI this spring.
    2010 Avalanche 4WD; AES 390; Mast LS3 heads; VVT Cam; ported TVS2300; Overdrive 8 rib pulleys; 2.7 snout pulley; ID1000; LS3 TB; WB 450; Twin MM cans; built 6L80; CircleD Triple Disk, CSR flexplate; Trucool 40K; Aeroforce Dual; AFX

  4. #4
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    You want a better idea of whether the observed error
    is offset error, gain error, a limiting / linearity error in
    order to correct appropriately.

    I recommend that you take at least three measurement
    sets - say, 0.000V out, 2.500 and 5.000 settings at the
    wideband, verified with a DMM at the wideband output
    to wideband ground (open circuit) and again with the
    whole wireball hooked up as-used.

    If 0.000 and 2.500 are dead-nuts and 5.000 is whack,
    it means you have a linearity problem and not an
    offset problem - and "fixing" offset for 5.000V will
    then jack your 0.000, 2.500V data.

    If it is a true, ground-loop offset then a significant
    part of that may be from WBO2 heater current,
    and heater current is ambient temp and load-point,
    time-at-load-point variable so today's sweet tweak
    is tomorrow's sour note. An instrumentation amplifier
    which takes its input signal and reference from
    inside the wideband (out of the current path,
    close-in to the output signal driver & its ref gnd)
    and its output reference from the EIO, could get
    rid of common mode offset. I've played a bit with
    this, you'd need an instrumentation amp IC and
    a pair of 9V batteries, or a single battery plus
    some regulators etc.; need to float the local
    supply to keep from adding yet another ground
    to the stew, etc.

    "Somebody" should have a look at the EIO cable
    alone, for applied vs reported channel voltage
    and input current vs input voltage.

  5. #5
    Tuner seven ends's Avatar
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    First 3 paragraphs I experimented with over the past few weeks. I had read your post about elsewhere on the non-linear treatment of the offset. I also read a thread (12Sec or 5Liter?) about being sure to have vehicle running for free air calibration and voltage checks (bung plugged). That increased the idle voltage from 4.96 to 4.97 at WB to EIO. Read elsewhere about AA battery test thru EIO to HPT with jumper in EIO signal to record raw voltage. This verification was dead on with multi-meter. At 4.97 this is fairly accurate output from the WB, my greatest error is with HPT recorded voltage which I believe the AA battery test and the improvement with heavier grounding prove out.

    Your lead-in on your 4th paragraph raises a new question I have not considered to this point and that is WB heater (power to ground, duh me). Good point to think about, thanks.

    As for the rest of paragraph four, that looks like a new hobby that might require some considerable commitment. Tabled for now but not forgotten.

    Your last paragraph.....the spot on AA battery test eliminated that one I think unless there is something non-linear happening in the EIO Interface on and it just happened 1.48 V was spot on. I have really been focused on grounding as the issue and your WB heater comment is a very good place to look next. Wow a forest. Thanks again.
    2010 Avalanche 4WD; AES 390; Mast LS3 heads; VVT Cam; ported TVS2300; Overdrive 8 rib pulleys; 2.7 snout pulley; ID1000; LS3 TB; WB 450; Twin MM cans; built 6L80; CircleD Triple Disk, CSR flexplate; Trucool 40K; Aeroforce Dual; AFX