1997 STS Ghostly Noise from Vacuum Leak?
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Northstar Engines and System Technical Discussion Discussion, 1997 STS Ghostly Noise from Vacuum Leak? in Cadillac Engine Technical Discussion; I have a 1997 STS that has been making a moaning noise that turns into a fluttering noise at random ...
  1. #1
    iconokrass is offline Cadillac Owners Member
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    1997 STS Ghostly Noise from Vacuum Leak?

    I have a 1997 STS that has been making a moaning noise that turns into a fluttering noise at random times. The noise is fairly loud and can be heard equally well inside or outside the vehicle. While driving, the noise seems to change with acceleration, getting much quieter when I let off the pedal, though still very noticable at a stop.

    I traced the noise to a hose that ends up in an "L" connector (like an old spark plug cap) that fits into a black plastic nipple (for want of a better word) on something that looks like an old distributer cap located to the right rear under the plastic shield over the intake manifold. When I remove the line (while running) the noise stops completely. The line is clearly a vacuum line of some sort and there is intense vacuum at the nipple.

    What I'm wondering is if there is supposed to be something between the nipple and the cap that is missing. The noise seems to be from air being pulled through the tiny gap between the nipple and the cap on the vacuum line, sometimes setting up a vibration that results in the fluttering sound.

    Help!

    Thanks.

    AB

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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    Under the cover at the right rear (looking toward the firewall) vacuum operated components would be EGR (Exhaust gas Recirculation) valve, FPR (Fuel Pressure Regulator) or maybe an A.I.R. (Air Injection) valve, none of which should leak vacuum even the tiniest bit.

    Can you take a digital pic, reduce the file size, and post it here??

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    iconokrass is offline Cadillac Owners Member
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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    Thanks for the reply. I will do that within the next day or so.

    The noise is driving my wife crazy...

    AB

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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    Right rear is the passengers side. That is where the EGR valve is.

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    iconokrass is offline Cadillac Owners Member
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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    Oh, well then left side; right if you are looking at the engine from the front of the car. The hose comes from somewhere around the firewall on the passenger side and ends up at this black plastic "nipple" on (as I said) what looks a bit like a distributor cap that is located at just about under the right rear (when looking at it from the front of the car--IOW on the driver's side) corner of the plastic shield that covers the intake manifold. I'll get a picture of it tomorrow and post it.

    Thanks for the help so far!

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    iconokrass is offline Cadillac Owners Member
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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    Okay, camera is not going to work for now, but I think I may be able to describe it all better now that I have taken a second look at it.

    What may have thrown you folks off was my description of what my memory said looked like an "old distributer cap." That visual came from some cross-wired whatever that I pulled from the 60 seconds or so I looked at the engine the other day.

    This may work better: There is a vacuum line (I am pretty sure that's what it is) that looks very much like an old spark plug wire with two "L" connectors on either end that runs from the passenger side near the firewall--but connected to an assembly that is jutting toward the firewall--along and underneath the silver plastic four-bolted cover that sits atop the manifold (or what looks like a manifold) and runs all the way to the right side (driver's side) of that cover to a small bank of three nipples, each of which has an "L" shaped hose running to it and the center of which this hose is attached with the "L" connector/cap. However, the "L" connector at the near end doesn't appear to be fitting tightly to the nipple, whereas the other "L" connectors in the same location are solidly connected. Following the hose back toward the firewall to the start point, I noted that the "L" connector there appears to have a clamp that affixes it to whatever it is attached to; no such clamp is on the near end.

    At best, the connection feels like a spark plug cap used to feel when the cap was over the plug, but not actually connected.

    A friend actually brought me the service manual from the local Cadillac dealership, but I can't figure out what to look under to find a diagram...

    I'll try again to find my digital camera tomorrow and get a picture.

    Thanks.

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    Submariner409's Avatar
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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    If that's the line that is leaking vacuum and possibly causing a hissing noise at idle, do what is necessary to seal the leak. Take the beauty cover off and idle the engine, listening for leaks with a rubber tube to your ear, similar to a stethoscope.......or buy a cheap one at Walgreen or maybe a Kmart.

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    iconokrass is offline Cadillac Owners Member
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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    I'm about 99% sure the leak and noise is coming from the cap itself. I located the noise before I even pulled the cover off and I can see the cap moving when the noise becomes the "fluttering" type. The cap actually seems bigger/longer than the nipple. If I squeeze it when it is in place, the cap collapses to some degree. All other similar-looking caps feel solid.

    This is why I mused that there may be something missing that is supposed to be in between the cap and the nipple; a valve of some sort?

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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    Go to a local parts store and look in the FRAM, PartsMaster, or Delco replacement parts catalog for your year car/engine and find the oil filter/air filter/PCVvalve/gas cap/etc. parts list.

    If your car has an actual PCV valve as opposed to a metered orifice, that rattle valve ($2.98) is what's missing.

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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    I am pretty sure the '97 did have a PCV valve, but it is mounted in the rear cam cover on the passengers side if I remember correctly.

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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    That's what I thought, and he's also talking about a tube connected to an assembly which projects toward the firewall on the passenger side.

    (My '02 has the orifice type, so I'm guessing at vacuum leak possibilities)

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    iconokrass is offline Cadillac Owners Member
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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    Okay, photos attached.

    The first photo is for orientation from the front.

    The second photo is closing in on the beast to the driver's side, just on the side of the manifold. You can see the three hoses attached.

    The third photo includes my fat, aging finger pointing at the center connector, the beast. You can actually see the suction pulling in the walls of the cap (the engine is running.) This is what makes me think something is missing.

    The fourth photo shows the cap removed.

    Ideas?
    Attached Images

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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    Ok, I am pretty sure that is the vacuum source for the PCV line. With the cap sucked in like that, it would make me think that there is a LOT of vacuum (plugged PCV valve). Pull the valve at the other end and shake it. It should rattle. If it does not, hold your thumb on one end and fill it with Gumout. Place you finger on the other end and shake it till it starts to rattle. Do this several times till the Gumout comes out clean, or just replace the PCV valve.

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    iconokrass is offline Cadillac Owners Member
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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    I think you guys have the answer. There is something on the far end of the hose that looks like a small valve between the connector and where it fits into whatever the assembly it is attached to (as you suggested, this may be the cam cover--I haven't looked at engines since cams were sitting inside the valve covers, so it didn't look familiar to me.)

    How does the other cap come off the valve--just pull? I don't have any Gumout, would WD40 work?

    Either way, I thank you for the help!

    I'll post again when I pull the valve off and fix it to let you know how it worked.

    Thanks again.

    AB

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    iconokrass is offline Cadillac Owners Member
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    Re: 1997 STS Ghostly Noise from Vacuum Leak?

    Whoops... That didn't work.

    I pulled the hose from the far end and pulled the pcv valve, but it sounded just fine (rattled great) and even looked new (I bought the car about 1 1/2 years ago.) I sprayed it with WD40 just to make sure things were loose. I also made sure the hose was not blocked.

    I put the valve and the hose back in place and there is still great suction at the near end and vibration that is creating the sounds. If I pushed the cap down on the nipple, the sound would stop, sometimes for a short time after I let it go.

    Also, once the sound was gone (just for the moment,) I could hear a strong hissing sound that was clearly coming from the same location...

    Since I know there is heavy vacuum (suction) at the nipple and, given your suggestion that something down the line must be blocked, seeing that there is still something stopping air flow from coming down the hose, but knowing the hose and valve are clear, this would suggest the blockage is actually PAST the valve, right??? And this would put it inside (or even past) whatever the assembly is the valve is attached to... right?

    Or, is the cap on the near end supposed to have a clamp like the one on the far end and without the clamp the vacuum pulls from the nearest higher pressure source (just outside the cap)...?

    Ugh...

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