Apu rough idle/blowing soot

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by "B", Jul 8, 2020.

  1. "B"

    "B" Bobtail Member

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    May 1, 2016
    San Antonio, TX
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    Ok, so I just got my Thermoking APU out of the shop, the belt was squealing and I had what I thought was an injection pump issue as well as an exhaust leak, after tightening the belt though it ran just fine with the bottom cover and top cover off with the intake filter out. Now that I have it back at my yard I turned it on so I could start cooling my fridge off to get ready to leave out tomorrow and now it won't run without bogging down and blowing black soot. To be clear it starts up just fine, and then bogs down when the compressor actually kicks on. I can check tomorrow and see if it runs without the compressor on but I doubt that's the actual issue as it ran fine without the casing on and the AC compressor actually coming on. Also no other services were done to the APU either. No fuel lines removed or oil changes in the past 20 days, and it was running fine other than the squeal and the exhaust leak Any ideas would be helpful.
     
    D.Tibbitt Thanks this.
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  3. D.Tibbitt

    D.Tibbitt Road Train Member

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    Apr 26, 2013
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    Is it shooting alternator codes? Thats what mine did when alternator was about to go out , would bog down when ac compressor kicked in... could also be a fuel pump but if it works fine otherwise i wouldnt think fuel pump would be the culprit
     
  4. reeferwrencher

    reeferwrencher Light Load Member

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    Aug 4, 2018
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    Run it without the air filter again and see what happens
     
  5. drivingmissdaisy

    drivingmissdaisy Medium Load Member

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    Its either a dirty air filter or a bad fuel pump or clogged fuel filter.
     
  6. 062

    062 Road Train Member

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    Oct 20, 2013
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    Could also be fuel shut off solenoid. Mine did the same a few weeks ago. To confirm you have to remove solenoid then start apu. To be able to shut unit off you have to put it back in the hole, then flip switch inside the apu to off. Watch what your doing because your hand isn’t far from flywheel.
     
  7. "B"

    "B" Bobtail Member

    47
    18
    May 1, 2016
    San Antonio, TX
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    It will continue to blow air after it sputters out and then throw the alt code. The fuel pump was replaced like 3 months ago by myself without running it dry, as I replaced the inside filter and fuel pump at the same time. I just bought a new air filter yesterday and installed it, so that isn't the issue. I will attempt to run it without the filter again, and then check the alternator. Mind you though with the ALT code being thrown it doesn't die and throw the code at the same time it dies and then like 4 minutes later it will throw the alt code and shut the blower off. It won't even try to restart.
     
  8. "B"

    "B" Bobtail Member

    47
    18
    May 1, 2016
    San Antonio, TX
    0
    Update, wont run even with the filter out, solenoid appears and sounds like it's working properly.
     
  9. reeferwrencher

    reeferwrencher Light Load Member

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    Aug 4, 2018
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    Crack the bleed screw on the injection pump and make sure it's getting fuel while fuel pump is energized like just before it cranks.Also turn the crank shaft on the ac compressor to make sure it isn't seized
     
  10. "B"

    "B" Bobtail Member

    47
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    May 1, 2016
    San Antonio, TX
    0
    Yeah compressor isn't seized, and it's 100% getting fuel, so pump is working properly
     
  11. reeferwrencher

    reeferwrencher Light Load Member

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    Aug 4, 2018
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    If it's getting fuel and cranking over then like the other guy said remove the fuel solenoid and see if it starts. The solenoid might might be pulling in ok but not holding, it has 2 circuits
     
    062 Thanks this.
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