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Engine shakes a little betw 7 to 9 rpm

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Edgrmndz, Sep 14, 2017.

  1. Sep 14, 2017 #1
    Edgrmndz

    Edgrmndz Bobtail Member

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    Feb 15, 2016
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    my 2012 Prostar MX13 at 600 rpm is fine but when I slowly gas it, it feels rough between 700 to 900 rpm then it smooths out. A mechanic put the computer and said all the injectors are running good he did the killing of each one and no problem there but he could not find the problem.
    In the morning all is ok runs smooth even when I do the slow increase of the rpm, when it gets to 700 to 900 is all smooth,,,but after running for an hour or so, it start going rough .
     
    Edgrmndz, Sep 14, 2017
    Edgrmndz, Sep 14, 2017
    #1
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  3. Sep 14, 2017 #2
    x1Heavy

    x1Heavy Road Train Member

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    Engines don't like running at 700 or 900. Have you set high idle during the night at say 1000? She should be a z generator at that rpm for sleeping.

    In normal driving between torque and high horse prior to red line there should be no misbehaving going on at it's working power band.
     
    x1Heavy, Sep 14, 2017
    x1Heavy, Sep 14, 2017
    #2
  4. Sep 14, 2017 #3
    Heavyd

    Heavyd Road Train Member

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    You probably do have an injector that is under or over performing in that RPM range but not enough to be detected. MF engines can also run rough at certain RPMs because they are choked off due to restricted exhaust,(plugged DOC or DPF) or partially open EGR valves.
     
    Heavyd, Sep 14, 2017
    Heavyd, Sep 14, 2017
    #3
  5. Sep 14, 2017 #4
    Edgrmndz

    Edgrmndz Bobtail Member

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    Feb 15, 2016
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    In the morning when I do this " test ". It runs smooth, perfect, no shaking, no rough . It it was an injector woul it do it under any condition?.
    We also cleaned, burned the dpf filters and put new sensors and new Dozer injector.

    I do this rpm checking,,when the truck is parked and in neutral,
     
    Edgrmndz, Sep 14, 2017
    Edgrmndz, Sep 14, 2017
    #4
  7. Sep 15, 2017 #5
    Heavyd

    Heavyd Road Train Member

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    Injectors usually miss fire worse when cold, and get better when warm, but it is just as possible for them to work fine when cold, and start to miss when warm.
     
    Heavyd, Sep 15, 2017
    Heavyd, Sep 15, 2017
    #5
    Edgrmndz Thanks this.
  8. Sep 16, 2017 #6
    skro47

    skro47 Light Load Member

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    Apr 26, 2014
    Québec Canada
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    Did you take the oil dip stick out?
    Just did injector orings and truck owner description of first symptoms was like yours. Check for fuel in oil and check oil psi gauge.
     
    skro47, Sep 16, 2017
    skro47, Sep 16, 2017
    #6
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