I have a 95 Blazer Vortec V6 and I have been noticing a hissing noise coming from behind the top of the engine near the firewall. Also when I shut off the car the hissing noise last for a few seconds and then stops (like a depresurizing noise). It is possible that there may be a vacuum leak somewhere behind the engine? Or could it be something else? If it is a vacuum leak, where should I look for problems (Its hard to see behind the engine). Thanks.

 

look for a foam hose near the firewall on the driver side, it should be connected to that plastic ball looking thing thats attatched to ur hood, basically the ball is sort of a cleaner for the vacuum and it also holds a little pressure after you turn the truck off, mine became detatched and i just tied the hose off as a temporary solution.

 

Had the same thing on my 94. Its hard to get at but right behind the distributor there is a junction of a few vacuum hoses and one of them runs into the back of the distributor. That one had a split and fell off.