I would check the overboost protection valve. Mine was plugged solid, so I never had any boost. Make sure the hose connections on the bottom & front are clear through with no power at the relay. Providing power opens both to the top port that should have a dust cap on it, but allows vacuum to escape.
Paul.

__________________
1984 300CD red/blk 290,000 partial resto
1980 240D 4 sp Brn/palomino gone
1997 Mazda Miata STO edition wife's baby
1988 Lincoln Mark VII LSC next resto
1986 Subaru GL wagon daily
1993 Isuzu pickup field beater
2008 Honda Civic EX-L 5sp wife's new car
1978 Honda XL350
1974 Honda XL70 my Calif. ride in HS