Hissing sound after turning engine off

Discussion in 'High Tech Retrofits' started by 75Maro, May 5, 2019.

  1. 75Maro

    75Maro Veteran Member

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    hey guys as the title says, when I shut the engine off there is a hissing sound coming from the engine. I think it’s coming from the air cleaner. 5.3 with a small cam. Runs great no issues just not sure what this sound is. Thank for any help.
     
  2. badazz81z28

    badazz81z28 Veteran Member

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    The radiator has a leak letting steam out? I can’t imagine a sound like that from the air cleaner, carb or FI?
     
  3. 75Maro

    75Maro Veteran Member

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    No coolant leaks, no fluid leaks at all for that matter. I will try and post a short video.
    Thanks
     
  4. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    Did you have the A/C running?
    My A/C does that as the high and low pressure sides of the system equalize through the orifice tube after the compressor turns off.
     
  5. Bandit723

    Bandit723 Veteran Member

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    Vacuum leak from the brake booster maybe?
     
  6. 75Maro

    75Maro Veteran Member

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  7. 75Maro

    75Maro Veteran Member

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    possibly vacuum? only heard after shutting engine off for about 3-4 seconds.
     
  8. xten

    xten Veteran Member

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    Sure sounds like vacuum
     
  9. 75Maro

    75Maro Veteran Member

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    crankcase ventilation maybe? exaggerated sound due to the aftermarket intake tube and cone filter?
     
  10. supwicha

    supwicha Veteran Member

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    Couple things come to mind. Bad check valve on your brake vacuum booster. Incorrect PCV system setup (block goes into a vacuum then vents after shut down due to vacuum source with no corresponding ventilation), IAC pintle opening during shutdown (if equipped), or TAC opening during shut down (may need a throttle relearn?). Defiantly sounds like a large amount of vacuum stored in the intake system returning to atmosphere. A short duration, usually .5 - 1 second is typical, this sounds extended. Is this a new motor? My worst prediction would be a leaking intake valve that is in the compression stroke during shut down that is passing by the valve under compression pressure, and venting into the intake.
     

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