Thanks in advance for any assistance rendered.

Have a 1989 F150 5.0, that when turned off has a noise sounds like air escaping. First thing I thought was maybe the power steering pump, but have checked that and the hoses seems to be fine. Any ideas what else to check. Trying to check all that I can before I have to take it somewhere to have it fixed.

 

Does it come with a slight hum/buzz from near the throttle body? If so, that's completely normal. It is the pressure sensor slowly acclimating itself back to no vacuum being pulled.

 

On our trucks (97 and newer) the vents in the dash are operated by vacuumed. I am not sure about your year. My first question is if this is a new sound (are you sure it did not happen before).
If you have the vents set anywhere other then defrost the default is for the vents to return to the defrost position. That may be what you hear, the sound of air entering while the vents return to defrost. I am not sure if that will happen every time you turn off the engine or if there is suppose to be a check valve on your vehicle.
One way to check this put the vent to the defrost position while running and see if it changes the noise you are hearing when you shut it down.

 

1989 F150, Settings on heater have no effect . Sound comes after it has run awhile then it is shut down. Was told by another to check the fluid level in the power steering pump, check for and repair leaks. Unfortunately this thing leaks everywhere right now so trying to localize it down to one area has not been easy. Going to steam clean the engine compartment now and see if I can't localize what is leaking and fix one at a time. Will make for a good weekend.

 

I've heard people say that the noise may be the pressure built up in the cylinder slowly escaping after the motor turns off... just a though.

-Sal

 

Well, after steam cleaning the engine compartment and tightening down almost everything, I have localized the problem down to a vacuum tree on top of the exhaust manifold. Will continue to troubleshoot when I get home from work.

 

Found the problem, Why the PCV valve is hidden behind and under the upper manifold, I haven't a clue. Felt behind the manifold toward the valve cover and found that the PCV valve was not connected. Seems that after I had some work done on the truck by Goodyear they did not hook back up the PCV valve. Won't go there again. Appreciate all the help and post from everyone, I learned alot in the process.