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Thread: Strange noise under load

  1. #1
    Join Date
    Oct 2011
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    Sydney
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    123

    Strange noise under load

    My recenlty aquired 97 V8 Auto is making a strange pinging/sweeking like sound when under load.

    At first I thought it might be pinging due to bad fuel, but Ive now run it on 91, 95 and 98 RON fuels from various suppliers and there is no discerable difference.

    Ruling out pinging as the cause, Ive checked belt tentions/conditions (as I thought it might have been a slipping or noisy belt) but couldnt find anything obvious there.

    I suppose the next logical thing to explore would be exhause leaks, as an exhaust manifold gasket might make a similar sound.

    So here is my quesiton, before I go searching for exhaust leaks, are there any other obvious or well know explinations for a pining like sound when under load?

    Looking to the experienced D1 guru's for guidance.

  2. #2
    Join Date
    Aug 2009
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    Sunbury Victoria
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    1,144
    It could be a leak in the exhaust manifold. It would be more of a tappet sound and mine goes away when it warms up. Also check all your leads, Dissy cap and rotor. You may be losing a cylinder under load. Being a low compression engine it runs fine a cylinder down but might give a pinging feel under load.
    Cheers, David.
    My Land Rover has made me a better Mechanic........
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  3. #3
    Join Date
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    did you mean a sqeeking sound? maybe check out your uni joints too.

  4. #4
    Join Date
    Jul 2010
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    pakenham
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    run your disco at night and watch your leads if you can see the spark running around then you need new leads, Another question would be you say the noise comes under load so is that when you labouring while going up a hill?? I have an auto disco too and it always made all sorts of squeaks and noises that no matter what i did it still made it. I just get concerned if it runs quiet now.

  5. #5
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    Oct 2011
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    Thankd Nico, Yes, its when going up a hill, or accelerating hard. Im startign to think its more to do with ignition timing. I have a feeling its too far advanced and I will check this out over the weekend.

  6. #6
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    10,496
    A sticking exhaust valve will jam under load and be most evident going up a hill.

    A loose sleeve will also be most evident under load when hot.
    Are you using water?

    Regards Philip A

  7. #7
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    Quote Originally Posted by shamat View Post
    Thankd Nico, Yes, its when going up a hill, or accelerating hard. Im startign to think its more to do with ignition timing. I have a feeling its too far advanced and I will check this out over the weekend.
    Check that the vacuum advance is working, Regards Frank.
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  8. #8
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    Quote Originally Posted by PhilipA View Post
    A sticking exhaust valve will jam under load and be most evident going up a hill.

    A loose sleeve will also be most evident under load when hot.
    Are you using water?

    Regards Philip A
    Starting to think its something like this as yesterday it over heated and even after a new thermostat, coolant cap and radiator flush ist still over heating! Suspect the cylinder is pressurising th colling system too much.

    Quote Originally Posted by Tank View Post
    Check that the vacuum advance is working, Regards Frank.
    Thanks Frank, I'll check that tomorrow (after referring to the manual as to what teh vacuum advance is)

  9. #9
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    Oct 2011
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    Finally had a chance to look at this in a bit of detail recently with a mechanic mate of mine. Everything mentioned so far checked out fine so we looked deeper.

    Turns out the sound is coming from within the exhaust, so I suspect a loose baffle or plate. When I remember, I will get under while its cold and bash the exhaust to verify the diagnosis.

  10. #10
    Join Date
    Oct 2011
    Location
    Sydney
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    Pinging/Chirping noise under load

    OK, so following up on an previous post (http://www.aulro.com/afvb/discovery-...nder-load.html) I still have had no luck at finding what is causing this pinging noise under load.

    I've not yet gone as far as stripping the engine down to check for moving cylinder sleeves etc as I am hopeful there is a much simpler answer.

    So far I know what its is NOT:
    1. It is not the fan belt - I did a quick test without the fan belt and the noise was still there (but the steering was ridiculously heavy!)
    2. Its not a timing issue as I've dialed it down to 6 deg BTDC and ran 98 octane and it still made the noise (its petrol only).
    3. Its not the leads as I've checked them all at night and no sparks etc. no interference with the radio or anything else to suggest it the ignition leads.
    4. Its not the exhaust manifold as I've done the "white paper" test and no leaks detected.

    The really strange thing is that it "sounds" like it is coming from under the vehicle as opposed to up in the engine bay. Could anything in the Auto Transmission/Torque converter etc make a metallic pining sound under load?
    Perhaps is in the exhausts itself?

    The auto shifts fine, even if it is a bit hard on the shift, and doesn't slip.

    Any though would be appreciated before I consign myself to a rebuild.

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