Intake manifold
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Northstar Engines and System Technical Discussion Discussion, Intake manifold in Cadillac Engine Technical Discussion; My cousins 93 STS's intake manifold is...Knocking...Never seen this before. The intake manifold itself is knocking. Like sombody whats to ...
  1. #1
    STSj90 is offline Cadillac Owners Fanatic
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    Intake manifold

    My cousins 93 STS's intake manifold is...Knocking...Never seen this before. The intake manifold itself is knocking. Like sombody whats to get out of the intake lol...I also hear a high pitched beeeeeeeeeeeeeeeeee...........Or somthing. I can put my hand over the intake manifold where i can feel the knock and hear it and put slight(NOT ALOT) pressure on it and it deadens the sound and goes away. It only goes away when i put my hand and put slight pressure in a curtain spot on the manifold. What is this? Temps were at 199 at this time. both noises are on the passenger side of the intake manifold from what i can tell. I didnt spend a whole lot of time messing with it...

    Is it a loose intakemanifold? Do we need to tighten it? The high pitched Beeeeeeeeeeeeeee isnt that loud at all...If you want me to discribe things more in detail for you. I would be happy too.


    The car is idleing smooth and is not skipping. Everything is perfect except for those damn noises.

    Oh yea, and you cant hear it with the hood closed. Yea, its not audable untill you open the hood. And to hear the slight high pitched noise you have to listen for it.

    Its the northstar engine.

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    Ranger's Avatar
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    Re: Intake manifold

    It has a vacuum leak. Try tightening it a little, not to much or you'll crush the gasket. If that does not work, replace the gasket. Not sure what the knocking is.

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    STSj90 is offline Cadillac Owners Fanatic
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    Re: Intake manifold

    Thanks ranger, Do we need to just tighten it on the side its coming from? Or all the way around? And do we need to do it while its running or?

    I wish somone could tell me somthing about the knocking. He's just called to see if i found anything out. So could a loose intake manifold or a intake leak cause the knock? Anyone know?

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    Re: Intake manifold

    I would retorque them all to spec's. No need to have the engine running while you do it.

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    Re: Intake manifold

    If there's a high pitched whistling, try moving the backfire valve a bit side to side with a long flat head screwdriver. My '97 made a heck of a whistling, this stopped it completely.

    I've never heard of an intake manifold knocking. Are you sure it's not the valves or the PCV valve? I've seen PCV valves flutter and make a tapping noise, but that's in the right bank cam cover.


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    Re: Intake manifold

    Maybe there IS a gremlin in there knocking with a hammer to get out. Open the manifold and take away his hammer.

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    Re: Intake manifold

    I have seen in the past working on other vehicles where something , like parts from a mass airflow sensor or other sensor parts breaking loose, and shooting past the throtle body in to the manifold.Also to check for a loose manifold gasket the old timers had it right , take some carb cleaner and spray LIGHTLY around the intake if you notice an RPM change then you have found not only the problem but the location at the same time! As for the knocking take the throtle body off the manifold, it is pretty easy even for a novice, take a look down in there and try a magnet wand if it is metalic this should catch it. This is the only thing I can think of. Let me know if this helps.

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    Re: Intake manifold

    This is a '93. The '93 & '94 have a removable intake cover. They can lift it off and have a look inside.

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    Re: Intake manifold

    Quote Originally Posted by Ranger View Post
    Maybe there IS a gremlin in there knocking with a hammer to get out. Open the manifold and take away his hammer.


    Good one Ranger! Good way to start my morning, with a good laugh!


    Need parts for your Northstar Engine? www.northstarperformance.com

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    STSj90 is offline Cadillac Owners Fanatic
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    Re: Intake manifold

    Yea, this is a 93. It has the removable cover like ranger said. We've been in there many times.


    As for the knock. It is definatly coming from the intake manifold. No where else. Im puzzled. I think that maybe, the intake manifold is so loose that its vibrating and making a knocking sound. I dont think theres anything loose in there. Its way to consistant for that, But we will open her up and take a look.

    If there's a gremlin in there. Ill put it in a bag and take some pics lol

    Ill def do some looking.... Thanks for the help everybody.

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    Re: Intake manifold

    Please do show us the pics of the Gremlin with the hammer! Best of luck finding the knock. Is there a loose bolt or a crack in the intake (it is aluminum on yours, right?) where the metal is moving back and forth to make that knocking sound? This is a tough one to figure out. Keep us posted with the progress/results.

    On a different note, here's one for ya. Pulled an engine from a 94 STS to do the HGs. Head bolt snapped off on the left bank, raised up about 3 inches from where it should be. The camshaft has a cast nub sticking out, and on every revolution, scraped against the shaft of the head bolt, and bent it over so far, that the head of the bolt punched a hole through the cam cover. This is how the car was delivered to me for repairs. I don't think I can trust that camshaft, much less the entire head. But that engine was making a knocking sound. Hopefully this is NOT what's wrong with yours. First time in approx. 50 engines that I've seen a snapped head bolt. I think it was a mechanic's mistake and left alone during a previous engine job.


    Need parts for your Northstar Engine? www.northstarperformance.com

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    STSj90 is offline Cadillac Owners Fanatic
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    Re: Intake manifold

    Quote Originally Posted by 97EldoCoupe View Post
    Please do show us the pics of the Gremlin with the hammer! Best of luck finding the knock. Is there a loose bolt or a crack in the intake (it is aluminum on yours, right?) where the metal is moving back and forth to make that knocking sound? This is a tough one to figure out. Keep us posted with the progress/results.

    On a different note, here's one for ya. Pulled an engine from a 94 STS to do the HGs. Head bolt snapped off on the left bank, raised up about 3 inches from where it should be. The camshaft has a cast nub sticking out, and on every revolution, scraped against the shaft of the head bolt, and bent it over so far, that the head of the bolt punched a hole through the cam cover. This is how the car was delivered to me for repairs. I don't think I can trust that camshaft, much less the entire head. But that engine was making a knocking sound. Hopefully this is NOT what's wrong with yours. First time in approx. 50 engines that I've seen a snapped head bolt. I think it was a mechanic's mistake and left alone during a previous engine job.
    Would hate that!^^^


    Ya know, Today we took his car for a drive and ran it HARD...And no more noises at all. Car runs great as always. It has around 196,000 miles on it and damn. Northstar engines sure do keep there power!!!

    Like i said there are no more noises. But we are not going to let it ride. We'll be doing some looking around at things. It can be put to the side at the moment tho. We can check the torqe on the manifold and if its not correct we'll correct it! We might even go ahead and replace the gaskets. But thats up to him. Its his car and money.

    Thanks for the help guys..

    And i think what happend is with all the WOT's we killed the gremlin. I thought i saw one fly out of the pipes!

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    Re: Intake manifold

    And i think what happend is with all the WOT's we killed the gremlin. I thought i saw one fly out of the pipes!
    Well he wanted out anyway, so he should be happy now.

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    STSj90 is offline Cadillac Owners Fanatic
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    Re: Intake manifold

    Quote Originally Posted by Ranger View Post
    Well he wanted out anyway, so he should be happy now.
    Haha, Yea! Probly hurt hitting the pavment tho!




    Maybe his little gremlin freinds wont decide to visit any other northstars.

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