I have the stock crank pulley (single belt kit) and a 4inch blower pulley. I've checked the actuator with a vaccum pump. Held 15 lbs the entire time I had it on there.

 

a 4" blower pulley will do that... you need to pulley down my friend.

 

I've ran 9 pounds with this exact set up before though. Then my boost level slowly started to decline over a course of a year. So I checked for leaks, couldn't find anything and decided to pull the blower and send it out to get it checked out. the blower was fine. rear rotor bearings just had a little play but their was no harm done to the rotors. but sence it was out i figured id get the whole unit freshened up. slap it back on and now cant see anything more than 4psi. this has been driving me insane.

 

Is the balancer pinned to the crank? Also, check for belt dust around the blower pulley - beside the dust, high pulley temperature after a run would indicate slippage. The belts I used to run were Dayco Polycogs and I am not even sure they are still available. Goodyear Gatorback belt grip very well but they have such low tensile strength that they overstretch and easily break.
For the purpose of testing you can disconnect the bypass valve solenoid vacuum line. The bypass is normally closed. Plug the vacuum line leading to the intake pipe. It may surge a little at idle which is exactly what the bypass prevents, but this would just be for testing.

 

I can't see a 4" pulley giving you 9psi. What are your cam specs?

 

My crank is not pinned and i have checked this before. crank bolt was nice and tight and had no sign of scuff marks or scraping marks on the back of the bolt head from the pulley spinning freely.
I have changed my belt already thinking that it was just slipping, but didn't fix the problem.
I have blocked off the bypass and already tested it that way already and drove it around to test it and got the same results.
Ive had a friend rev it in park while i watch the actuator arm move so i know it is working under quick light load, so their is no reason it wouldnt be working on a heavier engine load like accelerating.
Ive even hooked a vacuum pump up the the actuator to hold it closed while i drove it around to test it and still only came up with 4 psi.
Ive checked my boost gauge and swapped them in and out of my other car.
Im down on power and its really boring to drive this way.

 

engine is an untouched 2001 lq4. so it has a stock lq4 cam. in the summer it would normally run 8 psi but in the cold winter months i would see 9 psi almost 10 sometimes
ive sprayed carb cleaner around my intake manifold and around my the couplings just to see if the idle would change but got no results. i even tried looking for bubbles using soapy water. but that was kind of a waste of time.

 

The bubbles won't worn since your intake is in vacuum. You'd have to be making boost to see bubbles.

I'm really not that familiar with these units. Try a different pulley size and see if boost is the same

 

In my experience a stock 6.0 will not make 9psi on a 4" whipple pulley. I just realize you're not even the original poster of this thread.