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Rough idle & misfire

Discussion in 'GM 6.5 Diesel Engines' started by matuva, Jan 10, 2010.

  1. A K2500 suddenly sputter and loss power while suddenly running rough and blowing a lot of white smoke.

    Thinking about injectors quitting, the guy put on new stanadyne ones. No change.

    He puts on a known good injection pump, tried 2 different PMDs. Still rough iddle and a lot of white smoke, no change.

    The truck starts really easely, iddle really rough but is able to not quit. It will respond to acceleration and is able to rev up with no problem, but boy, it really smokes :eek:

    They called me and I hooked my laptop, and here's a screenshot of what I get :

    K2500 DTCs.jpg

    I'm not really sure I understand everything DTCs mean.

    Would you help me decoding them and give me your advice ?

    Thank you for that.
  2. NVW

    NVW Well-Known Member

    May 5, 2008
    Castor, AB.
    Matuva, did he recently fill up with fuel? Could be dirty fuel or water in fuel.
  3. Not recently, at least not just before the troubles occur.
    I have told him to check fuel.
  4. ak diesel driver

    ak diesel driver 6.5 driver

    Feb 7, 2009
  5. buddy

    buddy Active Member

    could fill out diagnostic checklist. Need more information.

    Is it always white smoke or ever black? No new noises? Ticking, did symptoms always stay same or change at all with new parts? Timing could be way too retarded. Does it run any better with ECT unplugged, not that the ECT is the problem. Or some air in the fuel system.

    Take snapshots of sensor data, timing data, fuel rate, etc
  6. I'll try to fill out the diagnostic list ASAP.
    For now, :
    • white smoke, unburnt fuel,
    • no special new noise or ticking,
    • TDCOffset : -1.41, desired & actual pump timing 10.1
    • no change with all new parts.
  7. buddy

    buddy Active Member

    I would try to eliminate air in the fuel system as a possibility, perhaps by running another fuel source straight to IP, instead of the system from the truck.

    Check to make sure the CPS isnt busted off its mounting tab and turned in its hole.

    Could be a PCM issue, as far as when its sending the inject signals to the PMD for the IP. Like if the CPS was not correctly positioned or PCM was going haywire. Or timing chain tooth was worn and jumped, if thats possible, so valves and injection are not opening at injecting at right time.
  8. Diesel -T

    Diesel -T Recruit

    May 9, 2008
    Maybe check compression reading on cyl 6 in particular.
  9. Veg_Out

    Veg_Out Walking J Designs

    Aug 20, 2008
    Boise, Idaho
    Along that line of a compression check...How about a pressure test on the coolant side of the house. Is there any pressure in the top hose when started cold?
  10. bk95td

    bk95td 6.5 nut job/addict

    Nov 26, 2008
    I would try to eliminate mechanical issues before blameing electronics.A compression test and visual check of the valvetrain would be a good start.
  11. bison

    bison Well-Known Member

  12. Finally found enough spare time to check this K2500 again. I have no compression gauge, but an old mechanic says I must pull out the passenger head. For him, one of the valves on cyl # 6 is blown.

    Does make sense to me. Will pull the head and see.

    Will let you know.
  13. Pulled the head, and found a damaged exhaust valve at cyl # 6.

    Should be fixed .
  14. ak diesel driver

    ak diesel driver 6.5 driver

    Feb 7, 2009
  15. buddy

    buddy Active Member

    Lets see some pics of that valve, and the piston top too
  16. Yup, I will shoot some pics and post.

    Valve seat and piston head are not damaged though, but it is the first time I see cracked valve that way :confused:
  17. OK, so, here are the pics :

    as you can see, the valve is broken on 2 locations
    exhaust valve.jpg exhaust valve1.jpg

    it looks like a kind of "coating" has failed, and (see arrows), the place were the valve seal on the seat valve is really worn.
    exhaust valve2.jpg

    Valve seat is almost fine

    Valve seat.jpg

    We also found a kind of "white material", like a kind of concrete on the top of piston, except in #6, which was probably washed by unburnt fuel...
    Valve trace.jpg

    that's the 1st time I see a broken valve that way...

    Attached Files:

  18. ak diesel driver

    ak diesel driver 6.5 driver

    Feb 7, 2009
    That looks like a delamination. Must be a manufacturing defect. Where did you find the pieces? I would have thought that they would have gone thru the port. I don't see any pits in the head or piston from pieces flying around either.
  19. The piece shown on pic just felt in my hand while checking the valve.

    The other one wasn't there, probably gone thru the port...
  20. ak diesel driver

    ak diesel driver 6.5 driver

    Feb 7, 2009

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