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cold start humming noise

Discussion in '2nd Gen. Tacomas (2005-2015)' started by TOMMCINTIRE, Aug 14, 2014.

  1. Aug 14, 2014 at 6:07 PM
    #1
    TOMMCINTIRE

    TOMMCINTIRE [OP] New Member

    Joined:
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    Tompaw
    Ft Worth Texas
    Vehicle:
    13 Tacoma 4cyl auto
    ON cold starts, even when outside temp is over 80 degrees, with the auto trans in park, ac and radio off, I get a high pitch humming noise that is pretty loud inside the truck. Seems to be coming from engine area, sounds like a noisy fuel pump, then after 15-20 seconds, I hear a loud "Crunch" noise from engine, and the noise immediately stops. (2013 4 cyl - automatic) 11,800 miles. Any suggestions or ideas on what the noise is. This is my 1st Toyota vehicle.
     
  2. Aug 14, 2014 at 6:20 PM
    #2
    nd4spdbh

    nd4spdbh Well-Known Member

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    smog pump air injection system... completely normal.
     
  3. Aug 14, 2014 at 6:26 PM
    #3
    TOMMCINTIRE

    TOMMCINTIRE [OP] New Member

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    13 Tacoma 4cyl auto
    Thanks !
     
  4. Aug 15, 2014 at 12:02 AM
    #4
    nine3

    nine3 Well-Known Member

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  5. Aug 15, 2014 at 6:26 AM
    #5
    OCNutty

    OCNutty Well-Known Member

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    Northern, Va.
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    Silver Prerunner DC v6 SR5 Tow
    I get the same noise; It appears that the system closes an air valve prior to shutting off the air pump. So what I hear is the humming for about a half minute, the a short rattling (you called it a crunch) sound (1 second), which is basically the air backing up into the pump causing this noise, then the circuit shutting of the pump kicks in, and it's off.
    With the engine running cold, I experimented by squeezing the rubber input hose closed (Simulate the closing of the valve), while the pump ran, and it rattled, released it and the rattle disappeared.
     

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