Engine knock
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Engine knock in Past Cadillac Vehicle Discussion; I have a 91 deville with a 4.9L. No check engine light on but it knocks during initial start and ...
  1. #1
    lackville91 is offline Cadillac Owners Member
    Automobile(s): 1991 deville 4.9L
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    Jun 2012
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    Engine knock

    I have a 91 deville with a 4.9L. No check engine light on but it knocks during initial start and warm up for about 30 seconds to a minute. Any ideas on what this is, oil pump maybe?

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  3. #2
    PineyJustice is offline Cadillac Owners Fanatic
    Automobile(s): 2001 deville base, 2008 dts
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    Re: Engine knock

    Is the knock at half or full RPM?

    Is there any irregularity to it or is it rythmic?

    Is it higher pitched and metallic or is it a dull thump?

    Need more information before anyone can give you any ideas.

  4. #3
    basscatt's Avatar
    basscatt is online now Cadillac Owners Master
    Automobile(s): 89 Coupe DeVille, 95 Sedan DeVille, 03 SLS, two 02 DHS's
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    Re: Engine knock

    Quote Originally Posted by lackville91 View Post
    I have a 91 deville with a 4.9L. No check engine light on but it knocks during initial start and warm up for about 30 seconds to a minute. Any ideas on what this is, oil pump maybe?
    -------------------------
    worn bearings are not uncommon in the 4.9 motor -
    the only solution is to replace them -

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with DTS floor shift)
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    Re: Engine knock

    Sounds a little like the "main bearing thump". Annoying, but relatively harmless.

  6. #5
    drewsdeville is offline Cadillac Owners Master
    Automobile(s): 2011 Crown Vic LX
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    Re: Engine knock

    I believe there is a TSB on the early 4.9's for piston slap. I think there was an issue with the intial design of the piston skirts (too short, perhaps?), and they were revised shortly after. Perhaps you have one of the engines affected.

    If you retain good oil pressure and the knock disappears within a minute, it's likely that this could be the problem (but don't assume, still need to confirm!). If it does turn out to be the source of the noise, it probably won't hurt much just to run it as is.

    The knocks you should be concerned about are the ones that occur/get louder once the engine is warmed up as those are almost always bearing knocks.

  7. #6
    cjmeyer is offline Cadillac Owners Member
    Automobile(s): 2005 STS
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    Re: Engine knock

    My 91 had same noise for the 40000 miles I had it and didn't seem to damage it

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