I just finished my hsw plate nitrous install along with many other projects and just started and drove the car for the first time today. After the engine is running and you shut it there is a hissing type noise coming from under the hood. I havent filled the bottle or sprayed it yet and I have tightened and double all the fittings. The nitrous is the first thing i thought of would do this.

It is possible it is some thing else let me know what you think.

 

how long does the noise last?

 

it last for a couple seconds

 

is it your ac...my ac you can hear hiss when you turn off the car

 

I dont have AC

 

Is it on a carb setup? If so, it's probably a leaky gasket in between the plate and intake or carb.