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Thread: LLY power loss

  1. #1
    Join Date
    May 2006
    Location
    Arizona
    Posts
    16

    Default LLY power loss

    Empty this "lly" truck runs fine, but mileage is still bad. 12 on the highway or in town, used to get 16+ in town and 19 on highway. My truck is having problems pulling 5,000 lb trailers and seems VERY sluggish. Mileage is down towing from 14 to 9mpg, so far clutch fan has been determined to be bad (temps had gone up some while towing) fuel filter seems to be fine and computer has issued no codes.

    Any other ideas what the problem could be? thanks
    2004 GMC LLY Duramax 2500HD CC SB 4X4

  2. #2
    Join Date
    Mar 2001
    Location
    Tolland,CT
    Posts
    118

    Default

    I guess this is where a boost guage would be good. My old 95 was down on power and smoked quite a lot. Finally found a bad wastegate solenoid and improvement was dramatic. I currently have a PO299 code and low tubo boost. I would hate to tow anything until its fixed (Mon. I hope). My light throttle driveability and mileage is still good though. Sure sounds like low boost could be an issue. How has the dealer been in responding? Maybe a different dealer is in order. Good luck!
    2005 Regular cab, LLY Allison, new 7/05

  3. #3
    Join Date
    Mar 2000
    Location
    Loyal WI US
    Posts
    10,792

    Default

    I guess the cat could be plugging. Have you had all ECM programming updates done?

    Another possible solution: http://72.22.76.69/tdpforum/showthread.php?t=23222
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

  4. #4
    Join Date
    May 2006
    Location
    Arizona
    Posts
    16

    Default

    Black95TD

    Gauages would be nice, but no, I don't have a boost guage. Truck is not blowing any smoke. So far dealer is still checking truck and I should hear something sometime today. Thanks for the reply.
    2004 GMC LLY Duramax 2500HD CC SB 4X4

  5. #5
    Join Date
    May 2006
    Location
    Arizona
    Posts
    16

    Default

    Kennedy,

    ""I guess the cat could be plugging. Have you had all ECM programming updates done?"" -- No, I have not had any ECM programming done, What updates are you refering to? I assume this is something the dealer does? Thanks
    2004 GMC LLY Duramax 2500HD CC SB 4X4

  6. #6
    Join Date
    Mar 2000
    Location
    Loyal WI US
    Posts
    10,792

    Default

    There are updates for surging, intake popping sounds, etc. I'd have them all done...
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

  7. #7
    Join Date
    May 2006
    Location
    Arizona
    Posts
    16

    Default

    thanks Kennedy,

    They "GM" claim all my updates were already up to date. Dealer replaced the Clutch-fan. Mileage coming home (25 miles) on highway was about 18mpg. Do you think they did updates and didn't tell me or would the fan cause this much drag on the engine?
    As far as power loss towing, I won't know the answer until I try to drag it up a hill. I'm still puzzled as to if all this could be the result of a bad clutch fan.
    2004 GMC LLY Duramax 2500HD CC SB 4X4

  8. #8

    Default

    My '05 LLY is similar. Runs fine, pulls fine, but mileage sucks compared to the LB7s. Granted, its bone stock, but what bothers me is that the mileage was good for the first 30-40K, then dropped off and won't seem to return.

    9mpg for the last 6,000 loaded miles. Thats a 26 gallon tank of fuel every 200 miles, folks...the good news is that it saves my lower back (get out and stretch) and I've caught two tires on their way down with road debris by stopping frequently and checking the trailer.
    2011 Chevrolet Tahoe 5.3L daily driver
    • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW, '05 Denali
    • Total GM diesel miles to date : ~950K

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