Hissing sound coming from engine
Thread Starter
Race Director
Joined: Feb 2008
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From: Maker of Sharp Objects, AL - Roll Tide
St. Jude Donor '10-'11-'12-'13-'14-'15-'16-'17
St. Jude Knife Maker
Hissing sound coming from engine
I have a hissing sound coming from my engine. Very loud and noticeable, and it doesnt really vary with RPMs. I'm thinking maybe an intake gasket, but what would cause that to go bad all the sudden?
Le Mans Master
Joined: Aug 2005
Posts: 5,375
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From: CA.
St. Jude Donor '13-'14-'15
Sounds like a vacuum leak--best way to check is to get some brake-clean and spray it around the intake manifold and all the hoses near there including the throttle body---If a leak is present the engine will try to die--Brake clean will not leave a mess as it dry flashes clean--another option is to use starting fluid--which will make the RPM's flare UP--
Pro
Joined: Jun 2010
Posts: 535
Likes: 0
From: CA
i agree with the above poster... sounds like you have a vacume leak. I would use a Propane Torch (do not light) and go over the intake to see if it jumps your RPM, if and when it does you found your vacume leak... as far as intake gasket going bad all of the sudden not sure, its a pretty beafy gasket. try to narrow down your hissing sound with the propagne torch and post back what you found
Thread Starter
Race Director
Joined: Feb 2008
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From: Maker of Sharp Objects, AL - Roll Tide
St. Jude Donor '10-'11-'12-'13-'14-'15-'16-'17
St. Jude Knife Maker
wouldn't the engine have trouble running if it had any type of intake or vacuum leak? It doesn't seem to run any different and the gas mileage is about the same.
Le Mans Master
Joined: Mar 2004
Posts: 8,700
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From: Ft. Lauderdale Fl
Sounds like a vacuum leak--best way to check is to get some brake-clean and spray it around the intake manifold and all the hoses near there including the throttle body---If a leak is present the engine will try to die--Brake clean will not leave a mess as it dry flashes clean--another option is to use starting fluid--which will make the RPM's flare UP--
Use starter fluid.
Pro
Joined: Jun 2010
Posts: 535
Likes: 0
From: CA
are you sure its not a tiny exhaust leak that your hearing, does the hissing go along with the RPMs or at least lower RPMs,,, like hisss, hisss, hisss, hisss, hisss or is it one constant Hissssssssssssssssssssssssssss
Last edited by 69SSC5; Aug 17, 2011 at 05:35 PM.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Adjusts very quiclky
However an after MAF vacuum leak may take some leaning for the ECM to compensate for it----the larger the leak--the longer it takes--A huge leak may cause the engine to die--but it dies by triggering other safety tables---( like min. RPM ) etc
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Tech Contributor
Joined: Aug 2008
Posts: 2,902
Likes: 21
From: Oak Hill Virginia
I had the exact same symptoms a while back. Prominent hissing sound (I suspected a vacuum leak) but the car ran pretty normal. It turned out that the little vacuum supply line off of back of my intake manifold had been broken the last time I'd removed the manifold... It runs from the back of the manifold down underneath the battery compartment... Sometimes a leaky battery will drip acid onto the lines beneath it and cause this problem; pretty easy place to check. Do all of your AC modes work properly? If you had this problem your ac would be blowing air out of all the vents all the time irrespective of what mode you have it set in. http://forums.corvetteforum.com/c5-g...with-pics.html
If you don't have that issue I would start by checking the PCV line off the right side of the intake (mentioned above) since it's so easy to check.
If neither of those fixes your problem then with the posters above. Brake cleaner works very well for finding vacuum leaks...
GL
If you don't have that issue I would start by checking the PCV line off the right side of the intake (mentioned above) since it's so easy to check.
If neither of those fixes your problem then
with the posters above. Brake cleaner works very well for finding vacuum leaks...GL
Last edited by cdkcorvette7; Aug 18, 2011 at 12:13 PM.
Thread Starter
Race Director
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From: Maker of Sharp Objects, AL - Roll Tide
St. Jude Donor '10-'11-'12-'13-'14-'15-'16-'17
St. Jude Knife Maker
depends how big of a vacum leak but in general yes the motor should run a little funny... usually idles irratic with a vacume leak. you say it runs fine, does it idle a little funny since the hissing started???
are you sure its not a tiny exhaust leak that your hearing, does the hissing go along with the RPMs or at least lower RPMs,,, like hisss, hisss, hisss, hisss, hisss or is it one constant Hissssssssssssssssssssssssssss
are you sure its not a tiny exhaust leak that your hearing, does the hissing go along with the RPMs or at least lower RPMs,,, like hisss, hisss, hisss, hisss, hisss or is it one constant Hissssssssssssssssssssssssssss
The idle isn't really erratic. It seems like it always has to me.
I still haven't even checked it. Maybe I can go out there this afternoon. Been getting home from work too late every day to look at it.
Safety Car
Joined: May 2008
Posts: 4,237
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From: Lacombe Louisiana
Also check your air bridge for cracks or loose connections.I perfer to use brake clean to look for leaks as it leaves no residue and with the wand is easier to narrow down a leak over propane.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Yeah--I'm always afraid that with propane if the car backfires i have a bomb in my hand !!! ( Sorry hank hill)---!!
Pro
Joined: Jun 2010
Posts: 535
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From: CA
If its a constant hisssssss then it sounds like u have a vacume leak either in the intake or before the intake. If u have a vacume gauge I would hook it up to the intake just to make sure do infact have a vacume leak.
Cruising
Joined: May 2018
Posts: 12
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From: Los Angeles CA
depends how big of a vacum leak but in general yes the motor should run a little funny... usually idles irratic with a vacume leak. you say it runs fine, does it idle a little funny since the hissing started???
are you sure its not a tiny exhaust leak that your hearing, does the hissing go along with the RPMs or at least lower RPMs,,, like hisss, hisss, hisss, hisss, hisss or is it one constant Hissssssssssssssssssssssssssss
are you sure its not a tiny exhaust leak that your hearing, does the hissing go along with the RPMs or at least lower RPMs,,, like hisss, hisss, hisss, hisss, hisss or is it one constant Hissssssssssssssssssssssssssss
Team Owner
Joined: May 2001
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From: Western NY
Cruising
Joined: May 2018
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From: Los Angeles CA
Drifting
Joined: Aug 2007
Posts: 1,846
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From: Orlando Florida
I am having this same issue with a 99 I just bought. Car runs and idles fine but there’s a constant hiss coming from the top of the engine somewhere. Guess I will try the brake fluid trick. I can’t believe the car is not running bad as much noise as it’s making.
Pro
Joined: Jan 2003
Posts: 638
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From: St. Johns Fl
Brake cleaner, not fluid!