Somthing werid happend today. i had to slam on my brake casue someone pulled out in from of me. then later i notice when i accelerate i hear a loug hissing sound . it only happend when i accelerate. NO CELS

the performace doesnt seem to be effected just a loud hissing sound

 

if its in the higher rpm you are ok.. mine does it to.. ive had it in many times and they say its fine... its just the intake, and GM's ability to restrict air flow..

 

evertime i press the gas pedel it makes that hissing sound i have a CAI and my car had never made that sound before.

 

Any Body ?

 

check your hoses to see if a vaccum line or something popped off.

 

checked as much as i could and didnt see any pop off also im not getting a CEL usally when a vaccum line pops off it will give me a CEL

 

check your aeroforce gauge for codes, sometimes i dont get a CEL but there are codes stored even after i clearem.

 

nope no stored codes

 

this happened in my moms silverado. only on the gas will it make the noise and she couldnt figure out why. so she took it in to the dealer and they said a front axle seal was leaking. so you could try that if you want but im just saying.

 

thanks ill have them check that out

 

Can you make the hissing sound out of gear? If so can you pop the hood and hear it? Should be able to trace it down that way. Does the hissing go away if you apply the brakes lightly when the sound is the loudest? Does the "tone" of the hissing sound change when you move the throttle?

I suspect the brake booster from what you wrote. It may be "Dealer Time"....

 

booster what do you mean by booster ? it doesnt make the sound at idle. but when i accelerate it mkae the the sounds

There are no performace issue assoicated with this. car still runs fine

 

The vacuum brake assist assy -- follow the large vacuum hose that comes out of the bottom of the intake manifold -- leads to the brakes at the firewall. The brakes are vacuum assisted. the hissing noise could be a leak at the valve or diaphram. Is the hissing more noticable under the dash or out-the-window? I'm not sure how Chevy did it on the SC cars but there is probably a vacuum pump -- I don't have the time right now to look into it, but if you don't find the problem I'll look through the service manual later.

 

with all the windows closed it sounds like is coming from the passanger side.

 

If you still have the stock down pipe, the flex joint could have cracked. I've seen it before. When you hit the brakes hard, the motor tilts forward. At idle or cruising it would be fine but under hard accel. it could leak.

 

well i am going to take it to the dealer weds but if that was craked would it throw a CEL

 

if you slammed on the brakes....depending on situations, you could have punctured your air filter...which would allow alot of air to be coming into that one small hole, hense a "hissing" sound.

 

good point but if i did i think i would have gotten a MAF high flow failure due to the amount of air coming in to the car.

it sounds like it might be exhaust too casue i can hear it when i rev the engine and when i press the gas pedal but like when i am just cruzing i cant hear it

 

At what RPM does the hissing start?

 

as soon as i touch the gas like when i start the car cant hear it wheni tap the gas i do. but when i put it in cruise control i dont hear it.

 

Let us know the outcome.

BTW, I looked up how the SC brake system is set up and it is similar to the 2.2/2.4 engines. Your vacuum brake booster takes vacuum from just behind the throttle body -- it's the large hose coming out of the top rear of the TB mount.

 

Someone made a good point about the flex pipe casue when i rev the engine i can here it and when i press the accelerate on the road i can hear it but no so much at idle

 

After you said you could hear it with while throttling-up it does sound more like an exhaust leak -- hard to tell from a computer.
You could try having someone take a rag and stopping up the exhaust at the outlet/tip, with the engine running, and then listen for a leak under the hood. Or you could do it yourself if you've got really long arms.....

 

i know i am taking to the dealer to have them take a look at it.

 

My car just started doing the same thing recently. If u find out post it id be happy to hear what the reasoning behind this noise is.