Strange Hissing Niose....6 hrs after ignition cutoff

[dogginfox]

I had to drive up and down a couple Forest Service Roads today (Wet, Gravel, Ruts, Ect.) I have been home for 6 hrs now and my 02 XLT has a strange hissing noise (Much like a nail was pulled out of a tire or a leaky air tank) coming from the passenger side of the motor somewhere around the alternator. The weird thing is that the truck has been sitting with no power since I got home!!!! I checked the tires and they all seem fine. I wiggled and jiggled as many hoses as I could easily reach with nothing to show for it.

Any clue on what could do this? everything seems cool to the touch on the motor. Im stumped

 

[X-North]

Leaking A/C system. That is the only thing that have pressure after the truck is stopped.

 

[nascar_intimid]

that's what I was going to say also, but that only has 12lbs in it I think. Is there a vacuum canister near the sound that could be leaking such as a charcoal canister for the fuel ventilation system...

 

[E.B. Cornburner]

The EVAP system goes into a self-test mode after the vehicle is stationary for a predetermined time. It'll energize the leak detection pump and pressurize the fuel tank, etc. to 1 PSI, then it looks for this pressure to hold for a predetermined time. If it doesn't, it'll set a trouble code. Sometimes if the tank still has residual pressure in it when you pop the cap to get fuel, it'll whoosh out all that excess air.

 

[Turdle]

Hmm
You might have kicked a tire into the vacuum reservoir globe , and cracked a plastic line, or knocked a line loose.