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Cummins 400 big cam 3

Discussion in 'Kenworth Forum' started by 84 Flattop, Apr 24, 2012.

  1. Apr 24, 2012 #1
    84 Flattop

    84 Flattop Bobtail Member

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    Mar 29, 2012
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    My cummins 400 big can 3 while at idle goes up and down 3/4 to 1 rpm all the time. I have new fuel lines and not old injectors, does anyone know what is causing this?
     
    84 Flattop, Apr 24, 2012
    84 Flattop, Apr 24, 2012
    #1
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  3. Apr 24, 2012 #2
    stranger

    stranger Road Train Member

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    You probably have the AFC screw backed out too far. That's the hex socket head screw above the throttle shaft. Does the engine rattle like crazy and blow black smoke when you stomp on the throttle? If so, it needs adjusting back in. Many times the engine will sound like it has a racing cam in it at idle when the screw is open too much.
     
    stranger, Apr 24, 2012
    stranger, Apr 24, 2012
    #2
    84 Flattop Thanks this.
  4. Apr 24, 2012 #3
    pillbox

    pillbox Bobtail Member

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    Apr 6, 2012
    santa rosa,ca
    0
    sounds like an air leak in the fuel system...check your fuel filter, make sure its tight.
    Big cam 3 motors were king back in the day.
     
    pillbox, Apr 24, 2012
    pillbox, Apr 24, 2012
    #3
    84 Flattop Thanks this.
  5. Apr 25, 2012 #4
    84 Flattop

    84 Flattop Bobtail Member

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    Mar 29, 2012
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    It doesn't rattle but black smoke yea which is what u want. What would be the lowest number button that you would suggest in the pump. By the way the filter is tight and all fuel lines.
     
    84 Flattop, Apr 25, 2012
    84 Flattop, Apr 25, 2012
    #4
  7. Apr 25, 2012 #5
    bender

    bender Road Train Member

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    A restricted fuel return will cause hunting at idle.
    If air is entering the suction side and hitting the pump the engine will also hang and be slow to return to idle.
    #10 button is very popular, probably a good choice.
     
    bender, Apr 25, 2012
    bender, Apr 25, 2012
    #5
    84 Flattop Thanks this.
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