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Thread: 2004 vs. 2007 3.8L (3800)... now lots of knock

  1. #1
    Senior Tuner 10_SS's Avatar
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    2004 vs. 2007 3.8L (3800)... now lots of knock

    Curious if anybody has a stock ~2007 Buick Lucerne 3800 file... I didn't see one in the repository. My 170,000 2004 Grand Prix 3800 seized up due to coolant leak into the oil, it ran great, no knock up until that point.

    I replaced it with a 50,000 mile 2007 Buick Lucerne 3800, it was almost a direct swap... only things slightly different were the oil pan and exhaust manifolds... The 2007 Lucern oil pan is cast Alum and a bit bulkier than the 2004 steel pan, so I had to grind 1/4" deep x 1" long area out of the bottom motor mount... that's it. The Exhaust manifolds are an updated design... they end up not needing replaced, but look a bit different is all.

    According to Autozone, all of the sensors are the same except the Throttle Body and injectors so I swapped those pieces.

    It started up and runs great, however now I notice I have 5-7 degrees of knock retard under acceleration, say 1/2 throttle mainly, before PE, around 90kpa and higher manifold vaccuum... I never had this before with the stock motor.

    Fuel trims look the same as the old motor for the most part.... little different but not more than 5-6% adding or subtracting...

    Any ideas? I wanted to look at the spark map on the 2007 Lucerne... wonder if the cam or compression is slightly different.
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    Whipple 2.9L, 3.875" Pulley, kit injectors, supplied MSD Boost-A-Pump, stock pump
    LG Motorsports 1 7/8" Headers - No Cats, stock mid pipe with JBA Axle Back
    ZL1 Wheels/Tires

  2. #2
    Tuning Addict 5FDP's Avatar
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    The cam and compression is the same, all L26's are all the same. Should be 9.5:1

    Just from what I've seen and read and been around, every motor is always different. Some rarely see knock and some just get it out of the blue but runs the exact same. Alot of the time people just bump up to the next fuel grade, so 89 instead of 87 and most of it goes away.

    What plugs are you running? Done a fuel system clean to maybe get rid of carbon build up in the newer motor?
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Senior Tuner 10_SS's Avatar
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    allright, thanks. I guess this is proof motors vary that much. It's super clean... here's a pic of the new vs old valvecover... the old one ran perfect, sounded perfect, no knock until it locked up. Guess I should have changed the oil.

    LOL

    ValveCover.jpg
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    Whipple 2.9L, 3.875" Pulley, kit injectors, supplied MSD Boost-A-Pump, stock pump
    LG Motorsports 1 7/8" Headers - No Cats, stock mid pipe with JBA Axle Back
    ZL1 Wheels/Tires

  4. #4
    Tuning Addict 5FDP's Avatar
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    Intake gaskets are killers, if never updated to the newest design it's a ticking time bomb.

    Most 2005.5's and up are the aluminum style and free of problems.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.