Knocking sound
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This is a discussion on Knocking sound within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hey everyone I recently bought a stock 05 wrx with 96k miles. It had a bad coil with misfires as ...

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    Knocking sound

    Hey everyone I recently bought a stock 05 wrx with 96k miles. It had a bad coil with misfires as a result so I replaced the bad coil and now the misfires are gone. But there was and still is a knocking sound when you rev the engine to around 3-4k...it sounds like its coming from around the turbo, downpipe area. I have done a compression test with great results (150 on all cylinders) so I'm wondering what could it be?

    Thanks guys any help is appreciated.

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    Registered User teflon_jones's Avatar
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    What exactly do you mean by a knocking sound? Does it vary with engine RPM?
    Scott
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    It doesn't have any sound of knocking when its idle but when I start getting up to 3-4k rpm I hear it and also when I take my foot off the pedal I hear it for a couple seconds. Its also constant when I keep the rpm at around 3k...the sound is constant and repeating. Not just a single sound like a piston slap. I've also checked the heat shield and its secure.

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    Subaru Newb MainFrame's Avatar
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    Stuck valve? I've dealt with a couple of these lately and it was kind of a banging noise that would go in and out depending on RPM..



    Get under the hood and rev it, if the sound is coming from the passenger side head I'd bet it's a stuck valve.




    You might also want to check your oil for metal.. just in case.

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    Registered User MakeItRoar's Avatar
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    Quote Originally Posted by miljkovicste View Post
    It doesn't have any sound of knocking when its idle but when I start getting up to 3-4k rpm I hear it and also when I take my foot off the pedal I hear it for a couple seconds. Its also constant when I keep the rpm at around 3k...the sound is constant and repeating. Not just a single sound like a piston slap. I've also checked the heat shield and its secure.
    Something in your turbo? 3Kish, when you hit positive pressure, your turbines might be doin' some monkey business.

    Is your OEM uppipe replaced? Catalyst in the turbo?
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    I just put it up on ramps and i heard it start to knock at lower rpm's when the car was under load. I don't hear anything when i slowly accelerate only when its under load (or accelerate more quickly). I tried to put my ear as close to where i thought its loudest and it sounds like its coming from around the 3rd cylinder. If the catalyst in the turbo was bouncing around wouldn't the clatter be kinda random? This sounds more to me like a metal knocking sound that's continuous but always the same as in its not random knocks...it follows the rpms. I will try checking the oil and try to inspect the turbo/uppipe this weekend. If I have to rebuild the engine..what would be the best route to take? Are we looking at like a $3k job? Thanks guys...

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    Registered User teflon_jones's Avatar
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    If it's coming from the area of a cylinder, I'd start to wonder if the rod was ok. A bad turbo or valve is more of a high-pitched noise of tapping/scraping. Knocking usually points to the bottom end or cylinder parts.
    Scott
    Past Subies - '11 STI Limited stage 1+ and '04 STi stage 2+
    '13 Wrangler Rubicon - custom front bumper w/12k lb winch & off-road lights, skid plates, diff guards, etc.
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    '77 F-150 heavily modded for off-roading

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    So I ended up checking oil and found no flakes...then took the Turbo off and there's lots of shaft play..I'm hoping that's it..I mean it has to make noise when it gets spinning right? The up pipe was intact so none of that got sucked in but the Turbo itself must make noise when it gets spinning rapidly...?

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