Cummins M11 Sounds Rough

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by TheBaron97, Jul 10, 2020.

  1. TheBaron97

    TheBaron97 Light Load Member

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    Jun 22, 2020
    Williston, North Dakota
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    Hey guys, I have a 1998 Freightliner Century class with a Cummins m11 in it. It started sounding/running rough about 5 months ago, and since then I've been trying to figure out what to do about it. I took it into the dealership in Williston North Dakota and asked them why it sounded so loud at idle and they said two of my exhaust manifold bolts were sheared off and missing from my exhaust manifold. They also did a RPM cutout test and said that two of my cylinders were just barely above spec and two of my cylinders were over spec. They said since two of my cylinders weren't producing enough power and two were overcompensating that it kind of evened it out and my engine was fine. So they ended up tapping out the exhaust manifold bolts and then changing the gaskets and putting it back together.
    The loud idle went away and it sounded and felt significantly better for approximately 3 days and then the sound came back. (Also I forgot to mention one of the reasons I suspected the exhaust manifold to begin with was because my turbo wasn't spooling up to its usual 26 psi it was only reaching about 24 and only very slowly).
    So after the noise came back I got on the exhaust manifold bolts with a socket wrench and was checking to see how tight the bolts were and some of them were hand loose. So I tighten them down but I didn't have a lot of room and I was on the job and I didn't have a torque wrench to put them at their spec 20 lb. So I just tighten them all down as best I could and kept running it.
    Fast forward a couple days I took it back to the dealership because of more issues I was having and asked them if they had to work the bolts down to spec and told them the sound came back after a few days and that some of the bolts were hand tight and they sent their shop hand out to tighten them down to spec and away I went, but the sound and the rough idling never went away.

    So that's the back story on it, since then I decided that Williston mechanics are ######## and decided to invest in about five grand worth of tools and do my own mechanicing from here on out. I've been running it for 4-5 months with a loud rough idle and it not getting more than 24 psi of boost. And I finally pulled it off to figure out what was wrong with it once and for all, but I'm not sure if I should spend $500 and replace the whole exhaust manifold or if my issue could lie somewhere else? It seemed like changing the exhaust manifold gaskets worked the last time for a short period of time. But it was a while ago and I can't exactly remember how well it actually fixed the problem or not. I sprayed down my turbos and exhaust manifold and everything that's under pressure with soapy water while I was idling but I couldn't see any pressure escaping anywhere and it seems like it would be making bubbles like an air leak if a boot was loose or the exhaust manifold gaskets were shot.

    I hope all this makes sense, every time I try to go back and edit things like spelling it messes around with my paragraphs and deletes things so it's hard to go back and edit this, basically right now my problem is I have a loud rough idle and my turbo takes a long time to spool up and doesn't go to its normal PSI and I'm wondering what the chances are that I can swap out my exhaust manifold to fix the problem and how I would know if my exhaust manifold is the problem. Or if I have some deeper engine issue that can be diagnosed a different way? I did do the bottle test to check for a bad head gasket and the RPM cut out test to check for other issues. I also sent in an oil sample a couple days ago and haven't heard back yet, but to be fair once they send me the results I'm not going to know how to read them to decide the state of my engine.
     
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  3. blairandgretchen

    blairandgretchen Road Train Member

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    Post the oil sample result here when you get it, I can help you read it.
     
  4. baha

    baha Road Train Member

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    You can measure the cam lobes with a end play tool to see if the rocker arms are lifting enough to be sure the cam lobes are'not worn down on any of injector lobes? and ex. and intake lobes?
     
    Last edited: Jul 11, 2020
  5. TheBaron97

    TheBaron97 Light Load Member

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    Jun 22, 2020
    Williston, North Dakota
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    Just got the oil sample analysis back from Schaefer's. It came back as "Normal" which I think is good because I ran the oil longer than I would have liked (close to 700 hrs). Here's a PDF of the results.
     

    Attached Files:

  6. TheBaron97

    TheBaron97 Light Load Member

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    Jun 22, 2020
    Williston, North Dakota
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    The engine still sounds rough and I am taking it into Westlie Truck Center in Williston North Dakota because they are already replacing the air compressor (which is under warranty). The head service tech said it might be the injectors and he said he could run a test on them. Is there anything in particular that I should ask him before he throws any parts at it?
     
  7. blairandgretchen

    blairandgretchen Road Train Member

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    ABA0568A-D08B-4215-95F8-759ADA8D71ED.jpeg

    That’s a real clean sample.
     
    Rideandrepair and TheBaron97 Thank this.
  8. TheBaron97

    TheBaron97 Light Load Member

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    Jun 22, 2020
    Williston, North Dakota
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    Westlie's took the valve cover off and tested the injectors and said that one injector wasn't firing at all and one injector was almost gone. They said it's be 4k for all new injectors and I told them to have at it. They also looked into my pistons and said that piston 6 had oil residue and soot in it and that my engine was creating some blowby due to some oil hetting burned but they said it wasn't that bad. They said it'd be a 40 hour job to remove the head and see if they could replace the piston rings deal that keeps the oil out.
    I don't want to spend 15k on a rebuild right now and if I'm not doing a rebuild it doesn't seem worth it to take the whole thing apart so I told them to just fix the injectors and call it a day. The truck and engine have 466,000 original miles. Did I make the right call? Also am I wasting money by spending 4k on new injectors when likely I may have to do a whole rebuild in the next year or so? How bad is it if my truck eats some oil?
     
  9. blairandgretchen

    blairandgretchen Road Train Member

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    Below is a running sample history for comparison.

    After looking again at yours - the soot is kinda high, but explained by that cylinder.

    Im not a mechanic, but I’d say replace injectors, oil - run a diesel treatment in fuel (I use Schaefer’s, but Howe’s will do), and go on.

    Oil at a gallon every 10,000 miles is fairly normal for these engines.

    More input from mechanics here appreciated.

    @Goodysnap ??

    C9CF5467-730E-4F98-885D-1B093BBB5983.jpeg
     
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  10. AModelCat

    AModelCat Road Train Member

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    Was #6 one of the cylinders with a failed injector by chance?
     
  11. TheBaron97

    TheBaron97 Light Load Member

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    Jun 22, 2020
    Williston, North Dakota
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    How'd you know? Yes cylinder six had a failed injector as well as being the one that has the oil seepage.
     
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