Engine Knock - Not Piston Slap

Discussion in 'GM Powertrain' started by fargo_182, May 9, 2010.

  1. fargo_182

    fargo_182 New Member

    Hey everyone.

    I have a 2003 silverado 4.8l 2WD
    Has 300,000km - so about 180,000miles

    Just recently started it up and it has this noise, like rocks bouncing around in a tin can.
    First I thought it was a rock in the heat shield of the CAT, but then I got a check engine light now. It is coming more so from under the engine somewhere, rather then the top of the hood.

    The piston slap I know of, and goes away after a few minutes. This sound on cold dtart is loud, but gets slightly quieter as I drive, and it warms up? But is still noticeable?

    Enging runs fine, I have all power still. Good oil pressure at 275kpa, Nothing that is different with the engine except this rock noise.
  2. rustyk2

    rustyk2 Rockstar 4 Years 500 Posts

    Is the knocking coming from the top end of the engine, or deeper in the engine? If its top end, could be in the valve train. If its deeper, it could be cam bearings. I'm assuming you would know crank bearings when they go, knocking does not quiet down or go away. Just something to check.
  3. Silverado Junkie

    Silverado Junkie Rockstar 4 Years 500 Posts

    What code did u get when the check engine light came on?
  4. fargo_182

    fargo_182 New Member

    It's coming from deeper in the engine. It still runs fine though? I'm assuming it's just a matter of time before it blows now....

    I gotta go get a code reader today to check it.
    Last edited: May 10, 2010
  5. Silverado Junkie

    Silverado Junkie Rockstar 4 Years 500 Posts

    well maybe something minor comes up on the code scanner but i cant think of anything minor that would cause knock like that.
    Last edited: May 10, 2010
  6. fargo_182

    fargo_182 New Member

    The code is P0420

    Does piston slap sound anything even like what I'm hearing?

    It almost sounds like it is in the exhaust near the headers. You know where two cats are. it sounds like a baffle or whatever in there is busted?

    I remember my old car doin this with a brand new cat, and it was inside? what you all think.
    Last edited: May 10, 2010

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