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Hissing Noise

 
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Old 08-02-2018, 01:18 PM
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Default Hissing Noise

I have a 2004 S Type. 4.2 base. I have recently noticed a hissing noise when the car is running from under the hood. I have attached a picture of an engine bay (NOT MY CAR) as a reference. When I put pressure on this piece, the hissing stops. Can someone please inform me of what this part is and the possible cause to the air leakage.
 
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Old 08-02-2018, 02:10 PM
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well, that is a photo of a supercharged car...same as mine...if your car has the same thing...that is the vent/filter for the pcv valve...it is under a constant vacuum from the intake manifold via the pcv valve....the hissing is the vacuum being created and passing thru that filter and the the hose and down the line...you may a have vacuum leak at the vent,,the hose connection or the hose itself...there is an o ring where the valve pops onto the engine and one where the hose connects...check those and also look for any cracks in the valve and hose...you can also hook in a vacuum gauge and verify your actual engine vacuum and see if it is out of spec...I know there is a way to spray something around the suspected leak and listen for an rpm change, but I do not remember what I used to use...maybe one of the other members will know...
 
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Old 08-02-2018, 03:30 PM
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Mine is not supercharged. I was unable to take a photo of my actual car but this vent is where the air leak(hissing) is coming from. I could tell that it is for sure coming from the Top of this vent. I took off the hose and the o ring was good. When I put pressure on this vent the sound stopped. Thanks for the reply
 
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Old 08-02-2018, 04:17 PM
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Check fuel trims. (There are hundreds of threads you can read...)
 
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Old 08-07-2018, 10:51 PM
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If you did not find the leak yet spray small amounts of wd 40 at the suspect area and listen to the idle...if it rises there is your leak....remember wd 40 is somewhat flammable so do not let it run down to real hot spots...best to do this on a cold engine warming up..finally remembered the spray technique
 
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Old 08-08-2018, 02:53 AM
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Originally Posted by scottjh9 View Post
If you did not find the leak yet spray small amounts of wd 40 at the suspect area and listen to the idle...if it rises there is your leak....remember wd 40 is somewhat flammable so do not let it run down to real hot spots...best to do this on a cold engine warming up..finally remembered the spray technique
this method will not work on modern fuel injected engines . As the idle does not rise .as you would expect .
due to the constant adjustments made by the PCM. Instead of the idle rising the computer changes the fueling values to compensate , which you can see whilst watching the fuel trims .
i can see why you would try this while the engine is cold and running open loop . As it would affect the idle maybe slightly but would be dependant on the side of the leak .
but you have only a short time to do so before the system switches to closed loop (chocke off)
The correct way to carry this out is to watch the fuel trims as you spray your flammables or non flammables at any suspect pipes or gaskets .
Wd-40 is to oily for this task you need a gas like either or butane or propane or an Inert gas.
Yes you can use inert gas as well as combustible gas To replace the air that is being sucked in through a leak in the intake system .both will alter the fueling values displayed in fuel trims .
 

Last edited by Datsports; 08-08-2018 at 05:10 AM.
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Old 08-08-2018, 10:16 AM
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Originally Posted by Datsports View Post


this method will not work on modern fuel injected engines . As the idle does not rise .as you would expect .
due to the constant adjustments made by the PCM. Instead of the idle rising the computer changes the fueling values to compensate , which you can see whilst watching the fuel trims .
i can see why you would try this while the engine is cold and running open loop . As it would affect the idle maybe slightly but would be dependant on the side of the leak .
but you have only a short time to do so before the system switches to closed loop (chocke off)
The correct way to carry this out is to watch the fuel trims as you spray your flammables or non flammables at any suspect pipes or gaskets .
Wd-40 is to oily for this task you need a gas like either or butane or propane or an Inert gas.
Yes you can use inert gas as well as combustible gas To replace the air that is being sucked in through a leak in the intake system .both will alter the fueling values displayed in fuel trims .
thanks datsports for the correction...i was thinking in terms of carb and old school stuff...forgot the ecm can compensate by the trims....i guess it would work in open loop mode because the ecm is not correcting things...maybe he will give it a try on a cold start ...maybe carb or brake cleaner as a spray huh
 
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Old 08-08-2018, 10:34 AM
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The trims are easy and work so why go to extra pain with stuff that is harder and may well fail????

From cold you have about 30 secs. Then you have to let the car cool again. No thanks!
 
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Old 08-08-2018, 10:45 AM
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Originally Posted by JagV8 View Post
The trims are easy and work so why go to extra pain with stuff that is harder and may well fail????

From cold you have about 30 secs. Then you have to let the car cool again. No thanks!
maybe he does not have a way to read trims and 30 seconds is a lot of time...just trying to help..not try ing to bag on someone else...seems like lately being helpful gets me rude replies
 
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Old 08-08-2018, 11:19 AM
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For a tiny cost ($5 up) an elm327 will do the job. Some of the other ideas will not or will mislead.

WD40 can get places you'd be better off it didn't go.

You can sometimes use a hammer to drive a screw in but generally I'd rather use a screwdriver.

I'm not having a go at anyone but at the same time it's better just to use what works and is reliable with no nasty side-effects.
 
 
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