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  1. #1
    Bobtail Member
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    cummins 400 big cam 3

    I have a 84 Cummins big cam 3 and when I idle at long periods at a time the motor smokes blue and when I take off it smokes a lot of blue for a few minutes and then it clears up. Can anyone help pinpoint the problem? I was thinking maybe the rack needs to be ran?


  2. #2
    Road Train Member bender's Avatar
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    They call that slobbering, it's normal. Low cylinder pressure and temp during extended idle periods allow some oil past the rings.

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    If you are going to be sitting any length of time the engine will not cool off when shut down.
    At an Idle, the engine is not producing boost and it is quit posible the smoke is from oil passing the valve guides, as well as unburnt fuel because the cylinder temperatures are low, and with no timing advance the injection is retarded.

  4. #4
    Light Load Member Round2's Avatar
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    My BC3 never did that, but it was new back then. I wish I had the power of that beast back. Those were hill climbing machines. Good luck with the oil issue.

  5. #5
    Bobtail Member
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    Thanks for the info. that makes me feel better about it. If that's normal then I shouldn't have anything to worry about. I'm gonna set the overhead this weekenditt may clear some of it up.

  6. #6
    Medium Load Member Starline's Avatar
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    Most all Cummins will slobber... If you let it idle long enough, you will see oil dripping out of the turbo or exhaust. My N14 slobbers as well when I idle at too low of an idle for too long.

    I'm I'm not mistaken, you should have a mechanical throttle lock or at least I have driven old mechanical cummin's that had them... just increase the idle to 900-1000 rpm's and you'll find that it doesn't slobber. Also it will be better for your engine as low idleing is the worse thing for diesel engines

  7. #7
    Bobtail Member
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    Blue smoke at a hot idle on that engine usually is a loose overhead. Setting the overhead is a great starting point. A worn camshaft will also cause it. A really blown out afc diaphram can allow fuel up the signal line into the intake & that can cause smoke as well. Take the signal line off the intake & look for fuel.
    Does the engine get up to 180 degrees?

  8. #8
    Bobtail Member
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    Yea it always runs at 180.

  9. #9
    Bobtail Member
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    I have noticed wetness around back of pump.

  10. #10
    Bobtail Member
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    Hey a Guy at a local garage told me for more power and better fuel mileage to put a #17 button and a purple spring in the fuel pump. For me I have my doubts on that, any suggestions?

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