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Thread: segment swap in COS5

  1. #21
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    Scratch the last thought, it seems like my Ohm reading and my 1.2v reading match up. The pcm uses variable voltage to interpret gallons and that all seems inline. So now I'm back to thinking its pcm/tune again. Maybe!
    '98 Z28 S475

  2. #22
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by B18B1LS1 View Post
    If I'm reading the electrical diagram correctly, I should be sending 5v down the purple wire to feed my sender, my multimeter is showing only 1.2v, hmmm. Does this fuel segment stuff affect the voltage being sent to the sender in any way?
    Which circuit diagram are you looking at (year/model/vehicle)...?

  3. #23
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    I only have the '98 manuals, 1998 Chevy Camaro v8
    '98 Z28 S475

  4. #24
    Lifetime Member Doc's Avatar
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    I take it you are using the 98 gage cluster? If so, the calibration of the fuel sending unit is about 180 deg out of phase with ( How it looks in the tune) the "newer" COS you are using. Had to play with road runner plenty of times setting up fuel sending units on fuel cells and other 98s.

    2000 Silverado Full Size 4x4: Forged 6.2, H/C F1R Procharger
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    www.eifalchemy.com
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  5. #25
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    Yes, 98 gauge cluster. I've tried scaling the calibration up/down/inverted just to try and get the gauge to move. But it seems no value affects it so far
    '98 Z28 S475

  6. #26
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    Wanted to update you guys, it's fixed! I'm embarrassed to admit it, but it was my fault the whole time.
    I pulled the pcm out (behind the dashboard) to backprobe the pins and see what was being sent to the gauge. Turns out there was no wire in that slot at all. When I did the pcm swap a long time ago, one of the instructions was "Red 36 to Red 38, Test First". I guess I took that as test the pcm swap and if it works don't bother with that wire. Since everything worked I had it bundled with the other unused wires and never gave it a second thought.
    Fast forward a few months later to now, when I went back to get the gauge working, I assumed a segment swap was all I needed. It never crossed my mind I had unused wires from the pcm swap.
    Moral of the story:
    CHECK YOUR WORK FIRST
    Thanks for all the help anyway guys!
    '98 Z28 S475

  7. #27
    Joe (Moderator) joecar's Avatar
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    Stuff happens... Thanks for the update.

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