rough running, about to sputter out

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by stonefly4, Nov 10, 2019.

  1. stonefly4

    stonefly4 Light Load Member

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    I changed the fuel filters and there is no apparent change in the problem. I can only assume that the problem is not due to contaminated fuel.

    When I dumped the fuel out of the used filters, it appeared clean. I have dumped fuel from filters in the past when the contamination in the fuel was very apparent.

    I'm quite sure I have a different problem.

    Perhaps a clue is that when I pull off the primary filter, I hear a gurgling sound. When I loosen the secondary filter, fuel gushes out. This makes it look like there is a lot of fuel pressure after the secondary filter but little pressure before the primary filter.

    Any ideas?
     
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  2. Rideandrepair

    Rideandrepair Road Train Member

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    Check the tank vent hoses, I guarantee there’s algae in those tanks, mine got crudded up in 7 weeks sitting this summer, cleaning them now. Used “ Killem” It took a week to start breaking it down, just changed filters, first time. Tanks are half covered in black slime, and half shiney clean. On my second tank now, dosed up good again with Killem, Howe’s and fppf, it’s going to take a while. Had this problem once before, never this bad, though.I think because it’s been caked on for a while, before I realized. I would take those anti siphon things off. You need to check with a flashlight for algae and bubbles n tanks, I’ve got both, running like yours, no boost at low end, fuel problem. Those hoses will crumble and fall apart, plugging filters. Maybe the primary’s just plugging up and creating the pressure in secondary. I don’t know, looking for answers myself. But new fuel lines , cleaner, extra filters, good place to start. Filters will catch the debris. Tanks will clean up.
     
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  3. stonefly4

    stonefly4 Light Load Member

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    How do you get 'em off.

    It looks like they're welded in there.
     
  4. stonefly4

    stonefly4 Light Load Member

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    I spoke too soon about the filters not helping.

    It took about 20 minutes. I don't know why. I had shut 'er down tryin' to figure out what to do next. A fellow working on his Cummins told me it was probably the fuel line running from the secondary filter up to the head. He said, "Fuel ain't gettin' to the injectors."

    When I saw how that line was routed, behind the starter motor, I realized there was nothing I was going to be able to do about it and still get the load delivered. I figured I'd bite the bullet and try and limp sputtering all the way to the receiver.

    When I started 'er up, she was running like a champ. I don't understand, but I ain't complaining. She ran so good I took another load. I bought more fuel filters along the way. I bought 4 primaries and 3 secondaries. That was 450 miles ago and she's still runnin' great. I put in two fppf Fuel Power when I fueled up in Auburn, ME. The spot I'm in is I gotta keep runnin' if I can. Now it looks like I'll be alright as long as I have the spare filters, and I'll keep adding algae killer and fppf like you been doin'. I'll clean 'er up on the go. It's all I can do. She's gonna get all new fuel lines, too.

    Thanks!
     
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  5. SoCalRed

    SoCalRed Medium Load Member

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    There was probably air it the system when you first replaced the filters and once you got going it cleared up.
    Main brings some bad memories for me , -20 below fuel started jellying. Nice folks up there helped me out.
    after a few more sets of filters you should be ok.
    Good luck.
     
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  6. Rideandrepair

    Rideandrepair Road Train Member

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    Glad to hear that!! Mines running better, but still something wrong. I’ve had that fuel line leak on both my 99 and current 2000, model. It’s a weak link. Both times, I ran a solid flexible fuel line, much easier and much cheaper than the flexible/steel tube hybrid original. I wrap it in 3/4 heater hose.
     
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  7. stonefly4

    stonefly4 Light Load Member

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    I don't think bad fuel or clogged fuel filters have anything to do with the problem.

    Question: Why, after running hard, and experiencing symptoms of fuel starvation, does the secondary filter gush out fuel under pressure upon being loosened with the fuel filter wrench?
     
  8. spsauerland

    spsauerland Road Train Member

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    Because primary filter is before fuel pump and secondary is after fuel pump.
     
  9. stonefly4

    stonefly4 Light Load Member

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    But the high pressure is there even after the engine is shut down. How is that possible?

    About 20 years ago I installed a one-way check valve on the output of the fuel pump because I had a problem losing prime. It worked. That explains why the high pressure in the secondary filter cannot escape back through the main fuel line. But why doesn't the pressure escape through the cylinder head back through the return lines? I checked for flow in the return lines at idle. I opened the return lines at the top of the tanks, and there is plenty of smooth return flow.

    What, then, exists inside the cylinder head that prevents the high pressure in the secondary filter from being released back through the return lines?
     
    Last edited: Nov 22, 2019
  10. AModelCat

    AModelCat Road Train Member

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    You've probably got a check valve on the return side too. Still need a small amount of pressure to overcome the spring in the check valve. Doesn't take much positive pressure to make a fluid spew everywhere.
     
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