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Thread: CALC.VET Struggles, VE Values Don't Seem Sane

  1. #31
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    I just did a review of my 411 install because I was missing a constant power wire, or so I think. I emailed Lextech to get clarification on that one as his document doesn't instruct you to add a 2nd constant power wire when 411 swapping a 97, but 98-00 actually have this wire in the harness and use it with the 411. At any rate, here's what I observed with the DMM:

    Battery: 12.21V
    C1-20: 12.21V (constant)
    C1-19: 11.48V (switched)
    C1:75: 11.68V (switched)

    So at this point I need to figure out how this truck is wired so I can narrow down where the voltage drop is. My gut says go right to the ignition switch, we'll see. At the end of the day I'm looking for a component that gets 12.21V in and spits out considerably less. Good call on logging voltage statesman! I'll have to add that to my list of stuff to watch.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  2. #32
    Joe (Moderator) joecar's Avatar
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    I have seen PCM is always 0.5 to 1.0 volts lower than DMM.

  3. #33
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    Quote Originally Posted by joecar View Post
    I have seen PCM is always 0.5 to 1.0 volts lower than DMM.
    I didn't even check the PCM with EFILive as I figured I had a smoking gun with that .5-.7V delta on the DMM switched vs constant. My concern with the discrepancy observed between switched and constant is that switched is what powers the injectors. Crap, I should have compared switched PCM vs the injectors now that I'm typing this. I know the injectors respond differently based on voltage, is that the concern here? Because the charging system itself was good to go way back when I initially checked it.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  4. #34
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    Quote Originally Posted by Supercharged111 View Post
    I know the injectors respond differently based on voltage, is that the concern here?
    You can tune out a voltage discrepancy as long as it's a constant discrepancy... my main concern is that your charging system is not working properly.

    Quote Originally Posted by Supercharged111 View Post
    Because the charging system itself was good to go way back when I initially checked it.
    If you're confident that the charging system is good, then don't worry about the voltage discrepancy. Personally, I'd be checking for resistance in the main power wire between the alternator and the battery. Even if you're happy with the ECM registering a lower voltage than your DMM... you should be concerned that your ECM voltage reading is showing your voltage dropping during WOT conditions.

  5. #35
    Joe (Moderator) joecar's Avatar
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    Check voltage drop between alternator and battery pos as statesman said, and also check voltage drop between battery neg and ground (at alternator body).

    If you have access to an oscilloscope, look for ripple in alternator/battery voltage.

  6. #36
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    Yeah, I didn't check anything under load. I was fixated on the wrong thing.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

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