INtake Manifold
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Northstar Engines and System Technical Discussion Discussion, INtake Manifold in Cadillac Engine Technical Discussion; Hello, I figured out today that my intake manifold is sucking in air. I guess this might be causing my ...
  1. #1
    akaz87 is offline Cadillac Owners Fanatic
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    INtake Manifold

    Hello,
    I figured out today that my intake manifold is sucking in air. I guess this might be causing my rough idle?? Its a 98 STS with 100k miles, do you think these problems are related? Is it hard to replace and how much?

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    Anthony Cipriano is offline Cadillac Owners Fanatic
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    Re: INtake Manifold

    How did you figure this? It's very unusual for an intake to be "sucking in air". If you spray water around the perimeter of the intake seal and can hear the water suck in and/or the engine suddenly smooth out then there may be a vaccum leak at a port seal. I'd remove the intake and inspect the seal before doing anything else. If it's a seal then it can be replaced or simply repaired locally with judicious use of RTV.

    The other potential source or an air leak or vacuum leak in the intake would be the pop off valve that's located at the front of the intake. Pop the little flapper valve open to see if it's sealing and if some piece of debris is caught under the seal. The pop off valve is replaceable sepately I think.

    In any case, a leak at the pop off valve would cause a whistling vacuum leak sound but not likely a rough idle. It would also possibly cause a high idle that the idle air control could not overcome but it shouldn't cause the engine to idle rough unless the leak were huge.

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    cadillacstars's Avatar
    cadillacstars is offline Cadillac Owners Member
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    Re: INtake Manifold

    I had a leaking intake manifold gasket, hard start, rough run when cold. best way to diag. remove and inspect. Sorry, but I do not think water should be sprayed around a suspect leaking manifold, may I suggest carb cleaner, propane, or brakkleen. water in intake bad. The "flapper valve" is available separately. personally I like to use propane to isolate vacuum / intake system leaks.

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    akaz87 is offline Cadillac Owners Fanatic
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    Re: INtake Manifold

    WEll I found out by putting some soapy water around the perimiter and I was smoking a cigar so I blew it into one of the vacuum lines. I saw the same comming out of the sides of the Manifold. I'm not sure if its the seal though, is it more likley the same is cracked rather then the manifold messed up? How much is the seal to be replaced? or is the seal part of the manifold?

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    Anthony Cipriano is offline Cadillac Owners Fanatic
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    Re: INtake Manifold

    Quote Originally Posted by cadillacstars
    I had a leaking intake manifold gasket, hard start, rough run when cold. best way to diag. remove and inspect. Sorry, but I do not think water should be sprayed around a suspect leaking manifold, may I suggest carb cleaner, propane, or brakkleen. water in intake bad. The "flapper valve" is available separately. personally I like to use propane to isolate vacuum / intake system leaks.
    Why not use water? I'm not suggesting a garden hose onto the engine but a spray bottle of water used to find a vacuum leak is far safer than spraying flammable liquids over the top of the engine and/or agressive solvents such as carb cleaner that can take the insulation off wiring or paint off painted surfaces. What exactly is "bad" about using water compared to the other products?

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    Anthony Cipriano is offline Cadillac Owners Fanatic
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    Re: INtake Manifold

    Quote Originally Posted by akaz87
    WEll I found out by putting some soapy water around the perimiter and I was smoking a cigar so I blew it into one of the vacuum lines. I saw the same comming out of the sides of the Manifold. I'm not sure if its the seal though, is it more likley the same is cracked rather then the manifold messed up? How much is the seal to be replaced? or is the seal part of the manifold?
    I'd take the manifold off and inspect the seal. It's pretty simple to do as there are no coolant passages in the manifold so it just lifts right off. Take out the 10 intake bolts and disconnect the fuel line and lift the manifold up. Possibly there is an injector seal that is cut/damaged that is leaking or it could be the seal around the perimeter of the manifold. As stated, if it's the seal around the manifold it can be repaired locally with some RTV if used judiciously.

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    akaz87 is offline Cadillac Owners Fanatic
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    Re: INtake Manifold

    Thanks for the advise. How easy is it to disconnect the fuel lines? This is the only problem that I am getting. I tired to put a piece of tape over the leak and it seems to get better, so there must be a leak in the seal then I think

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    Anthony Cipriano is offline Cadillac Owners Fanatic
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    Re: INtake Manifold

    There's a little tool that you can get at most auto parts stores to release the quick connect fuel line fittings on GM engines. With a little patience you can also release the locks in the connectors manually with a small screwdriver but the tool is sure and easy.

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: INtake Manifold

    Quote Originally Posted by Anthony Cipriano
    There's a little tool that you can get at most auto parts stores to release the quick connect fuel line fittings on GM engines. With a little patience you can also release the locks in the connectors manually with a small screwdriver but the tool is sure and easy.
    Ha! Little patience!? It took me a good 30 minutes to do with a screwdriver... I could easily get 3 tabs, but the fourth never made it. Next time I'm buying the $9 kit

  11. #10
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    Question Re: INtake Manifold

    I have a 1999 Deville when started the vehicle whistles. I've been told it is the Intake Manifold Gasket, Manifold and Seals. When taken to one shop the mechanic played around with the "flapper valve" and the noise stopped while car was running. I came here and now see that this part may be replacable seperately? If so, does anyone have a part number or specific name for the part? No one I call can seem to find it.

    Thank you!

  12. #11
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: INtake Manifold

    You're looking for a backfire relief valve or manifold overpressure valve. I don't have a '99 parts list.....there are two or more versions of the part.

    Cadillac dealer parts department.

  13. #12
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    Ranger is offline Cadillac Owners Member
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    Re: INtake Manifold

    I think the Tech Tips section has a parts list as a sticky.

  14. #13
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    Re: INtake Manifold

    My 98 doing the same thing. Checked the intake manifold and foung the bolts were finger tight or less. Tightened them and the problems went away.

    Bill

  15. #14
    mongongo is offline Cadillac Owners Member
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    Re: INtake Manifold

    Amen to that, Found the same thing when doing my starter!!
    Idle is great now, no jumping around at all.
    And I have freaking 215 thousand miles now.

  16. #15
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    AJxtcman is offline Cadillac Owners Connoisseur
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    Re: INtake Manifold

    Is the the area that was leaking?


    You can paint it like this.

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