07redMustang

Sometimes after I drive my car for 10+ minutes and shut it off I get this hiss under the hood. IT hisses for a good minute or so. Is this a normal sound or do I have a small vacuum leak somewhere? I've tried to pinpoint the location of the hiss but I can't seem to find it anywhere.

BM83

are you running the a/c when it happens?

Favre4TD

Im pretty sure if the motor is off you cant have a vac leak

07redMustang

It does it if the ac is on or off.

Isn't there still a vacuum even when the motor is off? I know there isn't anything producing the vacuum when the car is off but isn't it still there shortly after you shut off your car?

blackstang14

When I had a vacuum leak after installing the X, the sound went away as soon as I turned off the engine. It was more of a high pitched squeal than a hiss. I have heard that hiss before and it is usually after I am running my AC.

07redMustang

Okay I will see if it does it when I only run the ac or not.

Thanks

Steven6095

Mine is hissing too!!!!!!!
I will tell you now it is not AC related. Drove the other day with the windows down, no AC - pulled into garage, shut it off and hissing.

157dB

Its the compressed freon going thru the orifice.
There is still pressurized freon after you shut off the motor.
There is no manifold vacuum after the engine is shut off.
There is vacuum in the brake booster after the engine is
shut off.
Do you have a still pedal after the hissing stops?
If they still act like power brakes once or twice after
the engine is shut off after the hissing stops then its
not the power booster.
If they are very hard after the hissinf stops and the engine
is off, its a leaky brake booster or vacuum check valve.