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Mercedes- intermittent rough idle

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Freightlinerbob, Oct 14, 2012.

  1. Oct 14, 2012 #1
    Freightlinerbob

    Freightlinerbob Road Train Member

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    This has happened a few times lately, today the Check Engine light came on.

    After several hours of steady highway cruising I'll pull of and as soon as the clutch goes in and the engine returns to idle, it starts to run very rough, even sputtering. But it always accelerates away just fine and pulls good. No unusual smoke, good MPG, good power.

    Earlier today it was so bad that the light came on, but after shutting it off, it started fine, idled rough but ran fine otherwise. Engine light stayed off. Now it idles fine again.

    Any thoughts?
     
    Last edited: Oct 14, 2012
    Freightlinerbob, Oct 14, 2012
    Freightlinerbob, Oct 14, 2012
    #1
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  3. Oct 15, 2012 #2
    Pablo-UA

    Pablo-UA Road Train Member

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    I sugest injectors ore PLD units, may be a bit low supply pressure

    To be sure Use DDDL ore Mercerdes StarDiag to check smooth idle and impact time. Over 3% ore correction is not good (10% is limit).

    The cheapest thing you start to check is injector nozzles (visit any good diesel shop, they have injector testers).
     
    Pablo-UA, Oct 15, 2012
    Pablo-UA, Oct 15, 2012
    #2
  4. Nov 15, 2012 #3
    Freightlinerbob

    Freightlinerbob Road Train Member

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    Wondering, pure speculation actually, if this could be related to the constant throttle valve, because it almost sounds like the engine brake is partially on. I've been on the road for 7 weeks and unable to bring it to my mechanic and only trust one other shop in the road but have not been able to get in there.
     
    Freightlinerbob, Nov 15, 2012
    Freightlinerbob, Nov 15, 2012
    #3
  5. Nov 15, 2012 #4
    Pablo-UA

    Pablo-UA Road Train Member

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    CTV fault is usually related with MR 18 18 fault code - low boost pressure

    no exaust way out - no turbo speed
     
    Pablo-UA, Nov 15, 2012
    Pablo-UA, Nov 15, 2012
    #4
    VisionLogistics Thanks this.
  7. Nov 15, 2012 #5
    alex1010

    alex1010 Bobtail Member

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    Rough idle and lack of power at lower rpm. Check engine light coming on. Code appearing saying EC 128. Sounds as if the exhaust brake is coming on.

    Just took truck to our engine shop in Montreal. Put on computer and got code for injectors. Mechanic suspected problem is lack of fuel by engine noise ,and no fuel seen through the glass on the water separator.

    Started checking fuel pressure and result was bad. We had just got the fuel pump replaced yesterday by our local garage. That was almost the problem.

    The real culprit is the drive that engages the fuel pump , it is stripped and the pump slips.

    The front covers need to be removed and the drive replaced. Parts around $300 .00 and 10 hours labor to complete the job.

    Will let you know monday, but this mechanic is pretty savvy and young at that!

    • :biggrin_25517:
     
    alex1010, Nov 15, 2012
    alex1010, Nov 15, 2012
    #5
  8. Nov 30, 2012 #6
    Freightlinerbob

    Freightlinerbob Road Train Member

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    Well, I finally got home and took it to my favorite Detroit shop. It turns out that the code was for #1 injector reaching its limit to smooth idle, but they couldn't determine if the problem was the unit pump or the injector since the problem refused to surface while it was in the shop. So I told them to replace the injector at $200 & 2 hours labor and see if that worked before spending $800 on a unit pump plus labor. I've driven it 250 miles so far without problem. Time will tell.
     
    Freightlinerbob, Nov 30, 2012
    Freightlinerbob, Nov 30, 2012
    #6
  9. Dec 2, 2012 #7
    alex1010

    alex1010 Bobtail Member

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    Truck just ran 5000miles since the repair, all is well. The fuel pump drive was the problem. Changed the fuel pump while we were at it cost around $440.00 plus the core.
     
    alex1010, Dec 2, 2012
    alex1010, Dec 2, 2012
    #7
  10. Dec 3, 2012 #8
    Pablo-UA

    Pablo-UA Road Train Member

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    unfortunatly Mercedes do not use fuel pressure sensor and the only way is to put fuel temperature sensor, make metric fitting and use presure gauge. Over 1.5 BAR at idle is normal
     
    Pablo-UA, Dec 3, 2012
    Pablo-UA, Dec 3, 2012
    #8
  11. Dec 3, 2012 #9
    alex1010

    alex1010 Bobtail Member

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    Thanks Pablo.

    Our Mechanic found the problem quickly, there was not enough pressure at idle , when at high RPM the inertia just pulled the pump drive along a bit like a torque convertor, so the engine ran ok( not missing) , although getting weaker all the time, in thye end it would not pull under load.
     
    alex1010, Dec 3, 2012
    alex1010, Dec 3, 2012
    #9
  12. Dec 3, 2012 #10
    Pablo-UA

    Pablo-UA Road Train Member

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    it is not typical pump damage... really
     
    Pablo-UA, Dec 3, 2012
    Pablo-UA, Dec 3, 2012
    #10
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