Shortly after installing my new 3"downpipe I also replaced the vaccuum hose going from the intake to the valve cover. It's called the vent hose. I replaced this hose due to a lack of boost. After I installed it there still seems to be a lack of a boost.During 4th and 5th gear, the turbo will turn on at about 2,600rpm's but will shortly shut off. When in lower gears however, the turbo stays on but there is aloud hissing noise. Theres is no apparent leak on thehoses thatI can see. I'm not sure where else tolook or what the problem could be.

Thanks for any help.
Nick

 

There is an S shaped hose that connects the PCV valve to the underside of the intake manifold that commonly gets a split in it. Beyond that you'll need to do a pressure test on the system.