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Thread: diesel knock

  1. #1
    Sr. Apprentice
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    Default diesel knock

    My 5.3 Vortec has kind of a slight diesel knocking sound when I start it up cold. After a few seconds the sound is gone. The engine runs fine, oil pressure is good, no loss of power, it's not using oil or cooling liquid. Is this normal?

  2. #2
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    Davandy's Avatar
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    What brand of fuel are you using?
    Use always a good brand not Avia or something cheap.
    Peter Smet
    Haasdonk, Belgium

  3. #3
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    Default

    Euro 95 unleaded mostly form Q8.

  4. #4

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    Could be cold start piston slap. GM engines have had this problem for a few years. It's not considered harmful to the engine. Theres a TSB out about it.

    Another possibility is the oil viscosity. How cold are you talking about? Could it be cold enough that your oil isnt flowing properly for the first few seconds until it gets warm?

  5. #5
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    DutchTBI- like others have said this is a common occurance with the 5.3,and it doesn't signify anything bad.Your engine won't break.
    GM says-and it is grnerally accepted,since very,very few 5.3's fail early-is that carbon deposits above the top most ring.This carbon causes a piston slap like noise-maybe by the carbon/cylinder/piston rocking a little before the piston expands up to full size.I have heard that GM put the top ring a bit higher on the piston on later models to decrease the annoying noise.This was considered a HUGE deal the in 1st couple of years after the 5.3 was installed.Gm spent big $4 trying to find the cause,and did a fair number of buybacks to make the customers happy,and to pull apart the noisy motors.Gm discovered, but more importantly the 5.3 didn't fail despite the noise.
    If this is your problem-probably is-don't worry about it.
    Luck,
    Charlie
    PS-Why the TBI? I'm pretty sure the 5.3 is a more advanced FI.

  6. #6
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    Thanks, that sets my mind at ease!

    @tb10plus, cold is around 0-5 degrees Celsius, it's hardly ever freeses over here. The Dutch importer of GM-cars recommends 10W40 in the cars for european circumstances, so I use that.

    @ phoebeisis: The TBI is in dedication of my beautiful ex-car, an '88 Camaro convertible with the 305 TBI engine. That car was the reason for me to get involved in some american car forum ( f.a. www.thirdgen.org) a few years ago. Since I am from the Netherlands (Dutch) and drove a TBI, my nickname became DutchTBI. When I sold the car I decided to keep the name, just to keep the memory alive.
    Attached Thumbnails Attached Thumbnails camarorene3.jpg  
    Last edited by DutchTBI; 01-20-2008 at 07:55 AM.

  7. #7
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    I remember that one
    Peter Smet
    Haasdonk, Belgium

  8. #8
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    DutchTBI,
    Nice Camaro. I figured it was something like that!
    I hope the new Camaro "arrives".Funny the Camaro in its most powerful trim was always just a little bit quicker than the equivalent Mustang(usually got slightly better mpg also), but the Camaro died.I don't think GM counted on $3.25 gasoline when they redesigned it.If they stick with it,maybe someday it will come with a 3.5 lt TDI(a straight 6 would be nice) with 250 hp,and 400 lb-ft,and get 30 mpg highway.You Europeans have plenty of TDIs-we don't have any worth speaking of(MBs,and maybe a VW soon).
    Thanks,
    Charlie

  9. #9
    Jr. Engineer Gmcsuvguy's Avatar
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    Thumbs up

    The knock is from carbon deposits in your cylinders, you can take the spark plugs out and pour in combustion chamber cleaner onto the top of the pistons and let it soak for up to 3 hours (not any longer or the carbon will start to solidify again). Disconnect your fuel pump and ignition system and crank over your engine (put rags over the spark plug holes to catch the spray). Reinstall your spark plugs and reconnect ignition and fuel system, start your vehicle and drive the hell out of it until the white smoke stops coming out of your tailpipe. This will help. You can also add a can of combustion chamber cleaner to yourfuel tank everyonce and a while to help clean it. Hope this helps.

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