Pete 379 1995 Detroit S60 Tachometer

Discussion in 'Trucks [ Eighteen Wheelers ]' started by blairandgretchen, Feb 18, 2018.

  1. GrapeApe

    GrapeApe Road Train Member

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    As others have said, you have a tach sensor in the flywheel. Loosen the jamb nut, screw it all the way in until it hits the flywheel, then back it off 1 turn and tighten the jamb nut. With the engine running, it should have an AC voltage. If it doesn't the sensor is bad. If it has voltage, plug it in and check for that voltage at the tach plug.
     
  2. countyrebel05

    countyrebel05 Bobtail Member

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    Mine was jumping and would come in and out if you hit it then finally died. Weight of the harness broke the solder connections inside. I took the chrome bezel off resoldered it and works fine. Also running a 95' 60 series in a 379. Made sure to the the harness up this time so it won't do it again.
     
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  3. blairandgretchen

    blairandgretchen Road Train Member

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    Ok - scan guage reads and tach does not.

    Do you mean harness weight on the guage, or bell housing sensor?

    Got it, thanks.

    So, if scan from ECM is fine, then it’s the bell housing sensor?

    I’ll try this tomorrow - how many volts AC are we talking?

    Again - is this the harness to guage weight we’re talking here?


    Thanks for the help guys, have a brand new guage and no go . . . GRRRRRR.
     
  4. GrapeApe

    GrapeApe Road Train Member

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    I don't remember, but it's not about the voltage, you only need a minimum amount. It's the frequency that the tach decodes in to an RPM. The flywheel has 118 teeth (if I remember right). For every 118 Hz you have 1 RPM, 118 kHz hertz is 1000 RPM.
     
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  5. blairandgretchen

    blairandgretchen Road Train Member

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    Ok. Sensor has 250 ohms resistance, I backed off jamb nut , screwed it in, and backed out a half turn.

    Now, old guage reads, but low - (500 when it should be 1500), and the new guage sits at zero.

    118 tooth count seems to be correct, both the old guage setting and the new instructions call for the same rocker switch calibration settings.

    So - still stumped.
     
  6. E model Cat man

    E model Cat man Light Load Member

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    Check the plugs at the sensor and usually is another connection on the ditch side near the heater hoses on the firewall. They have to be perfectley clean where this us a feed and return A/C setup. Also might take the sensor out and check the magnetic tip pickup to see if its intact.
     
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  7. GrapeApe

    GrapeApe Road Train Member

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    That is puzzling. Reading low sounds like dip switch settings, but I can't tell you why the new one doesn't work.

    I have a 2000 Pete here with a Detroit and the sensor in the flywheel, this is what Pete shows for switches:
    DIXSON ELECTRONIC TACH CALIBRATION
    SWITCHES CLOSED- 2;3;4;6;7 - TACH

    That's different than the pic you posted, won't hurt to try those settings.
     
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  8. blairandgretchen

    blairandgretchen Road Train Member

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    A buddy suggested this too. Probably should have done this while I was under there.
     
  9. blairandgretchen

    blairandgretchen Road Train Member

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    This is an Amtek 900 series - It says

    “If the vehicle has an electronic engine, set 5 and 6 to on, and the rest to off”

    I tried this setting, no go, and then defaulted to the above settings you listed , which were the same as the old tach settings too.

    Back to the sensor and wiring.
     
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  10. blairandgretchen

    blairandgretchen Road Train Member

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    Ok.

    Pulled the VSS from bell housing. Tip intact and no damage, save a little dirt. Bench tested 250 ohms, tested a new VSS for comparison - same.

    Getting 250 ohm at the tach head, so wiring all good.

    Same results - old tach reads flickety and low, New guage no reading.

    GAAAAAAAAAAH!!!!!!!!
     
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