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Old 12-05-2010, 07:12 PM
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Engine Bay Noise

What's up guys got a really strange noise I canít track down. Here's the deal, I drive a 2002 with the 4.7, quadra drive and up-country suspension. After sitting over night I start the car and start driving. After I hit 2nd gear or sometimes around 15 to 20 MPH I get a rattle from the engine bay, it high pitched. The noise will change with RPM but only does in gear and moving. If I throw it and N and rev I get nothing. After a min of driving itís gone. I have tried everything, cats, heat shield, lines rubbing, ext. Has anyone heard of or experienced this? Call me crazy but when I do pull over and pop the hood i hear the PCV valve rattling like hell, replaced and cleaned entire intake still does it. Any suggestions welcome, Thanks.
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Old 12-05-2010, 08:50 PM
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Re: Engine Bay Noise

Can it be a leak from one of the exhaust manifolds?
When you talk about the rattling noise, are you sure its from the PCV valve? I have never heard the PCV valve making any sound.
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Old 12-06-2010, 09:10 AM
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Re: Engine Bay Noise

Thanks for the reply, but it is defiantly not an exhaust rattle. Totally different kind of noise. I started the jeep today started down the road and threw the car in N. I live on a bit of a hill so I let gravity take me down the road. Got to the end put it drive and not a sound. When i did hear the noise I jumped out and popped the hood. I removed the oil fill cap and plugged the PCV valve hole with my finger and the valve stopped rattling around. Could be obsessing over the wrong thing but Iím going nuts with this one. Going to disconnect the PCV tomorrow morning and give that a try, I know it sounds odd..
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Old 12-06-2010, 10:09 AM
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Re: Engine Bay Noise

When the PCV valve rattles, or the valve has to be replaced, or there is a pulsating suction. (the valve should rattle when shaking it by hand, but never heard that it rattles during operation) I would start changing the PCV valve, its quite cheap. Take care to remove the rubber hose with care from the PCV valve, otherwise the PCV valve breaks easily. (happened to me). Its easier to remove it with the engine hot, then the hose is more flexible, or heat the hose with some hot water.
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Old 12-06-2010, 01:01 PM
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Re: Engine Bay Noise

I have replaced the PCV valve twice already. First I thought i had a bad one so i went back to AutoZone and grabbed another one. Still did it. Being completely obsessive i went to the dealer and got a factory one, still does it. So i thought maybe there is not enough vacuum to pull the valve open. So i cleaned the entire intake and hoses checked the vacuum pressure and there is plenty of suction. Clueless.. It may be something else altogether but it a very different noise than all the other usual belt, pulley, heat-shield or exhaust, engine or tranny noise I have ever heard. Thanks for the responses, Iím lost at this point.
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Old 12-06-2010, 01:43 PM
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Re: Engine Bay Noise

The PCV valve gets its vacuum from a point downstream of the throttle body. The hose which connects to the resonator box is only connected to the 2 cylinder head breathers. Are you sure that the vacuum at the PCV valve is constant. If for example the vacuum supply fitting is almost blocked, opening of the PCV valve could result in colapsing the vacuum, letting the PCV valve to get closed again. This could result in a vibrating PCV valve. So i would check the tubing from the PCV valve to the point where it connects into the inlet duct for partly blocking or kinks. If ok, check the manifold fitting if that is (partly) blocked. Jeep manual says to use a 1/4 " drill by hand to remove any debris from the opening. You need to use a mirror to find this manifold fitting, it points towards the firewall
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Old 12-06-2010, 07:51 PM
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Re: Engine Bay Noise

I will give that a try and let you know how I make out. Thanks for the help.
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