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6nz Cat erratic idle....

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by rbrtwbstr, Apr 23, 2019.

  1. Apr 23, 2019 #1
    rbrtwbstr

    rbrtwbstr Road Train Member

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    I currently run a Western Star glider with a 6nz CAT, 475HP, engine build date is 2001. Every once in a while, when I start it, after a minute or so, the idle speed will jump to 1000 rpms. The only way I can get it back to normal is by moving the truck. Then, once I stop again, after a minute or so, it goes back up to 1000 rpms.

    I had the fuel temp wire on it, but I've removed it since this began, and it still does it. And I know it used to idle up a bit to 800 rpms when it was cold, but it would return to 600 as soon as I would push the clutch.

    Any ideas?
     
    rbrtwbstr, Apr 23, 2019
    rbrtwbstr, Apr 23, 2019
    #1
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  3. Apr 23, 2019 #2
    Cam Roberts

    Cam Roberts Road Train Member

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    Fuel wire is not causing this. Sounds like some sort of short somewhere in your main engine harness. You check for any stored codes using your cruise control switch? What is the condition of your wire harness
     
    Cam Roberts, Apr 23, 2019
    Cam Roberts, Apr 23, 2019
    #2
  4. Apr 23, 2019 #3
    Intothesunset

    Intothesunset Road Train Member

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    Have your pedal looked at could be the TPS sensor is bad.
    I wonder if that engine was programmed to run high idle when parked?
    If your engine were cutting out and not throwing a code I would suggest looking at the injector drivers they can come loose and no code will show.
     
    Intothesunset, Apr 23, 2019
    Intothesunset, Apr 23, 2019
    #3
  5. Apr 23, 2019 #4
    rbrtwbstr

    rbrtwbstr Road Train Member

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    Yeah there's no codes showing, the truck is a year old, so I imagine the wiring harness is still good. It works just fine, other than this issue. Our mechanic is stumped on it as well. He said he's gonna ask our local Cat guru about it
     
    rbrtwbstr, Apr 23, 2019
    rbrtwbstr, Apr 23, 2019
    #4
  7. Apr 23, 2019 #5
    Intothesunset

    Intothesunset Road Train Member

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    If it is a Fitzgerald glider. I would question their workmanship.
    Maybe the harness got damaged from rubbing?
    Or a short somewhere?
     
    Intothesunset, Apr 23, 2019
    Intothesunset, Apr 23, 2019
    #5
    MM71 Thanks this.
  8. Apr 23, 2019 #6
    rbrtwbstr

    rbrtwbstr Road Train Member

    3,210
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    Jul 11, 2012
    in the bush somewhere
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    Not a Fitzgerald. Built in our shop, so I'm pretty confident the wiring isn't rubbed or pinched, but you never know.
     
    rbrtwbstr, Apr 23, 2019
    rbrtwbstr, Apr 23, 2019
    #6
  9. Apr 23, 2019 #7
    KittyKicker

    KittyKicker Light Load Member

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    Don't assume the wires are still good. I have a 389 glider that had light issues about 6 months after I bought it. Turned out that a harness had rubbed on the bottom of the cab...
     
    KittyKicker, Apr 23, 2019
    KittyKicker, Apr 23, 2019
    #7
  10. Apr 26, 2019 #8
    Bigrigmayo93

    Bigrigmayo93 Light Load Member

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    Maybe a speed sensor? My 03 c15 would give rpm issues while driving. That fixed my problem.
     
    Bigrigmayo93, Apr 26, 2019
    Bigrigmayo93, Apr 26, 2019
    #8
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