hissing noise

[dellstopjeep]

when my jeep 1990 4.0 xj 4dr is running there is a hissing noise, it has always been there, my neighbors 1989 4.0 does the same thing, does anyone know what that is?? :huh:

 

[90NHXJ]

Where's it sound like it's coming from? It could be a vacuum leak. Also the fuel pump in the gas tank can be noisy.

 

[SouthernXJ]

Gonna have to crack the hood and stick your head in there while it's running. Does it increase when your RPMs increase or is it steady?

 

[89xj]

when my jeep 1990 4.0 xj 4dr is running there is a hissing noise, it has always been there, my neighbors 1989 4.0 does the same thing, does anyone know what that is?? :huh:

from engine bay or rear??????? my crystal ball is broken.

could be vacuum leak. brake booster could be leaking.

from the rear, it could be the fuel pump.