I posted a while back ago because i had an annoying hissing noise coming from the driver's side engine bay. it started right after i got done installing my headers. i expected an exhaust leak because of a broken manifold bolt (the one by the firewall). when i removed the gasket i found that there was no sign of leakage. i put a new factory gasket on but the noise is still there. Does anyone have any other ideas on what it could be? Its only when i give it a little gas around 1600 rpms. When i put it in neutral and coast, it goes away....even when i give it gas. so please, any opinions. Thanks

 

Vacuum leak? Brake booster or PCV? Doesn't fit really since you say it goes away when in neutral.

 

Hm?

Vacuum is strongest at or close to idle. You never know.

When the motors cold and hissing, spray short little bursts in the suspected areas and listen for rpm changes.
I say cold because the stuff is flammable. If you have e-fans you can turn them off while cold also.
Snoop is a soapy water in a nice squeeze bottle with a small extendable tube to apply to suspect areas. If it blows it will bubble. If it is vacuum it will disappear.

If you have a AM catch can installed they are noisy anyway. Pinch the hoses before and after the can and you will hear it stop. Listen to an OE newer corvette under the hood and you will hear it there too. You can pinch your hoses to see if it drops out there too.

You could have a split hose or plug at the connection rotated where you cannot see it.

 

I replaced my pvc with the newer fixed orifice before i did my headers. Do you think that could have anything to do with it? I also have 89000 miles on the truck and still running stock plugs. Could that have anything to do with it. I have also heard that aftermarket headers will produce more valve train noise. Its just an annoying noise that you can hear when you give it a little gas in overdrive.

 

If you removed your plugs, check all of them for tightness.

 

I don't know if the fixed orificce did it for you or not. I cannot hear mine in the cab.

 

mine hisses after i turn it off.

 

mine does it. it was doin it from the factory.. it sounds to be comming from the driverside of the intake man. i was told its just high pressure fuel line.. i havent had any idle or running problems so i believe them.. just my .02

 

make sure you do not have any hoses or lines hitting your firewall....if you do it will pipe the noise right into the cab.

 

yep pretty much sounds like what i have... i never think twice about it, just like the ticking..