I installed an Autometer boost/vacuum gauge last weekend and I'm wondering if I the car has a vacuum/boost leak. What are the normal readings? I get about 14 inHg of vacuum at idle and about 19-21 inHg under deceleration. Boost gets up to about 15 psi at 5,000 rpm under WOT. I've read that this boost reading is fairly normal.
However, under steady partial throttle and boosting, say 5 psi, the boost will slowly drop to 0 psi. If I press the gas pedal down, the boost will increase, but if it's steady, the boost will drop. Id this normal?
I also hear a hissing/sucking sound when I shut the car off as the vacuum readings go from 14 inHg (since it's idling) to 0 inHg.
I should mention that I did the VGS mod a couple months ago and left a capped tee accessible so that I wouldn't have to remove anything this time. I don't remember this hissing when shutting off the car. If it matters, the car is an 04 with the JCW engine kit, 15% pulley, and an Alta intake.
Any ideas/comments? Thanks!

 

sounds right to me I just installed a scangauge (calculates boost off the map reading) my vaccum is around -10psi full wot around 6k rpm I get 15.6. cruising I hardly see any boost until I blip the gas. Also I have heard the hissing sucking sound ever since I installed my alta intake.

not sure this helps. just saying sounds like your car is behaving just like mine does.

 

Thanks, that actually helps. I'm getting the impression that everything is the same but now that I can see the actual numbers on the gauge, the sounds seem strange. I may need a stiffer spring on the BPV to cure the dropping boost under steady acceleration.