Cummins N14 miss at idle

Discussion in 'Trucks [ Eighteen Wheelers ]' started by jsbiohazard, Feb 21, 2020.

  1. jsbiohazard

    jsbiohazard Bobtail Member

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    Feb 21, 2020
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    I am chasing a miss at idle again with my cummins n14. It is in a 98 fld120 425hp It will miss and sound like the motor is kind of loping after it warms up for a few minutes. It is pulling real good but sounds bad at idle. I have replaced the ecm, injector harness, and 5 injectors in the last 3 months. The 6th injector is 1 year old. When I unplug each injector, they all seem to make a difference in idle but I know that this is not the correct method since the Insite program isolates the amount of fuel going to each injector when doing the cutout test. I think that maybe I have an injector that is over fueling possible and causing the ecm to compensate fuel supply to other injectors but I dont know how to isolate this . If I set the idle up to 1000rpm it will run a little rough for about 3-4 seconds and then clear up and run smooth. I have been reading this forum for years and finding solutions from everyone's input but this is my first thread because I cant find where someone else has had this particular issue. Thanks in advance for any help
     
    HopeOverMope Thanks this.
  2. ChevyCam

    ChevyCam Light Load Member

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    Have you replaced the engine position sensor? Driver side right behind the air compressor.

    Seems like it could be worth the shot, sensor is only 45-50 bucks.

    Problem with Cummins N14
     
  3. I glide 47

    I glide 47 Road Train Member

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    If one's overfueling. And you increase rpm turbo boost up and compensate for over fuel problems go away! Only miss are idle ,how long since last over head?
     
  4. J.R.

    J.R. Bobtail Member

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    The old they all do that, cause they do. Wal-Mart 2 cyl oil 1 gal to 150 gal sure helps mine.
     
  5. jsbiohazard

    jsbiohazard Bobtail Member

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    Feb 21, 2020
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    I ran overhead last week and cleaned filter on fuel pump. It was clean already. Fuel lines have been replaced within last year. I run ATF in fuel once every two weeks to break up any carbon.
     
  6. jsbiohazard

    jsbiohazard Bobtail Member

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    Engine position sensor was replaced 3 months ago but I could try again and if no difference Ill keep it as a spare
     
  7. boneebone

    boneebone Road Train Member

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    Check the pass thru’s, the wiring gets old and brittle.
     
  8. jsbiohazard

    jsbiohazard Bobtail Member

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    When I put the new injector harness on it came with new pass thru connectors but I will check if any of them are taking oil.
     
  9. Heavyd

    Heavyd Road Train Member

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    I would check for aerated fuel, or low fuel pressure next.
     
    SAR Thanks this.
  10. jsbiohazard

    jsbiohazard Bobtail Member

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    Feb 21, 2020
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    fuel pressure is 150 at idle and 170 when at 1500 rpm
     
    ChevyCam and baha Thank this.
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