Vacuum leak somewhere inside the dash
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HT4100 4.1, 4.5, 4.9 Discussion, Vacuum leak somewhere inside the dash in Cadillac Engine Technical Discussion; Hey everyone how are you I fixed one vacuum leak at the pcv valve and have another somewhere behind the ...
  1. #1
    mike93 is offline Cadillac Owners Fanatic
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    Vacuum leak somewhere inside the dash

    Hey everyone how are you I fixed one vacuum leak at the pcv valve and have another somewhere behind the dash anyone have this poblem and know where it's coming from before I tear everything apart? thanks

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  3. #2
    drewsdeville is offline Cadillac Owners Master
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    Re: Vacuum leak somewhere inside the dash

    Can you estimate as to WHERE behind the dash? There are a few vacuum operated items back there including the climate control and parking brake release...

  4. #3
    mike93 is offline Cadillac Owners Fanatic
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    Re: Vacuum leak somewhere inside the dash

    It's like somewhere around the radio or ashtray in that area

  5. #4
    Ranger's Avatar
    Ranger is online now Cadillac Owners Member
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    Re: Vacuum leak somewhere inside the dash

    Snoop around down there with a stethoscope. A vacuum leak will sound like a hurricane.

  6. #5
    mike93 is offline Cadillac Owners Fanatic
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    Re: Vacuum leak somewhere inside the dash

    ok and yeah when your in the car with the radio low you can really hear it

  7. #6
    ehall's Avatar
    ehall is online now Cadillac Owners Connoisseur
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    Re: Vacuum leak somewhere inside the dash

    Probably a leak at the HVAC control unit. Outlet selection is typically controlled by a tangle of vacuum lines.

  8. #7
    steelybill is offline Cadillac Owners Enthusiast
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    Re: Vacuum leak somewhere inside the dash

    A length of hose, like 3/8" fuel hose etc works good to listen for localized leaks. Just be careful with your ears!!

  9. #8
    mike93 is offline Cadillac Owners Fanatic
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    Re: Vacuum leak somewhere inside the dash

    Ok thanks it's wierd because when i have the deforsters on the car idles erratic and could that be why I don't have heat?

  10. #9
    ehall's Avatar
    ehall is online now Cadillac Owners Connoisseur
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    Re: Vacuum leak somewhere inside the dash

    I haven't looked at the FSM but typically the outlet baffles are controlled by vacuum harness from the HVAC control unit. If the baffle for the defroster selection is broken then it could suck air into the intake (vacuum is created when pistons pull air and fuel into combustion chamber), and this could cause erratic idling as the MAP sensor tried to adjust for changes in air pressure. I wouldn't think the vacuum draw would be that high (typically the HVAC control knocks it down quite a bit) but if it's around 5 hg inches then it certainly could. Only way to know for sure is put a vacuum tester on the harness and see what happens--they cost $20ish at any parts store, behind the counter with other testing tools.

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