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Thread: Help Diagnosing Rough Idle

  1. 12-16-2016 #1
    thoridian
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    Help Diagnosing Rough Idle

    I have a rough idle that rears its ugly head primarily when the weather gets cold. During the summer it is fine, but as soon as winter sets in the idle gets so rough it shakes the whole truck. Ran a few scans to get balance rates and they look fine when in gear, but the balance rates don't read when in park the idle gets so rough so no idea what the balance rates are when the idle is acting up. What I can see is that the fuel and injection rates start dropping to 0 during the rough idle but the pressure remains relatively stable. Any ideas what might be the cause? I have attached the logs, any help in pin pointing the cause would be greatly appreciated.
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    2005 Silverado 3500 LLY, 4" turbo back exhaust, S&B CAI with S&B turbo mouthpiece
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  2. 12-18-2016 #2
    GHuggins
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    Goes away when a load is applied usually points to the dual mass flywheel going bad - that's if your auto has one - they were hit and miss... I've seen many a sets of injectors replaced because of misdiagnosed flywheels... Usually you can put a load on the engine via the trans then put it back into neutral when the problem is present - if the vibration is gone for a few moments then slowly returns - it's usually the flywheel...
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  3. 12-22-2016 #3
    Programmer
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    LLY ? I had the same problem with mine in the winter. Fine in PN--rough and smoking in gear. Is this what you have ?
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  4. 01-26-2017 #4
    thoridian
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    Quote Originally Posted by Programmer View Post
    LLY ? I had the same problem with mine in the winter. Fine in PN--rough and smoking in gear. Is this what you have ?
    Yes, that pretty much sums it up.
    2005 Silverado 3500 LLY, 4" turbo back exhaust, S&B CAI with S&B turbo mouthpiece
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  5. 01-31-2017 #5
    thoridian
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    The weather warmed up enough to get some decent logs of the balance rates. I averaged the values I got for balance rates and the main fuel rate and did a few calculations to account for the main fuel rate in the balance rates per the post on dieselplace.com found here. Looks like I am looking at a full set of injectors unless anyone here has any other ideas on what might be causing my rough idle and blue/white smoke. Smoke is not coolant, first thing I checked.

    Injector Balance Rate Results (31 Jan 2017).xlsx
    2005 Silverado 3500 LLY, 4" turbo back exhaust, S&B CAI with S&B turbo mouthpiece
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