Here's what I found on it...looks like you might have your hooked up backwards.
GM Boost Control Solenoid:
Port 1: Silver plug, by itself on one end.
Port 2: Opposite port, next to port 3
Port 3: Comes with a small filter on it.
I don't believe the solenoid is polarity sensitive.
At rest: Port 1 and 2 allow air to pass. No air can travel from Port 1 to 3, or 2 to 3.
Energized: Port 2 and 3 allow air to pass. No air can pass from 1 to 2 or 1 to 3.
Port 1: To turbocharger, or optionally another line on the compressor side.
Port 2: To wastegate
Port 3: Back into intake, after the MAF.
Port 3 (optional): Just vent to atmosphere, but you should put a filter on it in case of reversal of flow. The GM solenoid comes with a small filter on this port out of the box, so just leave it on if you wish to port to atmosphere.
How this works...
At rest, the solenoid allows the wastegate to see all boost pressure.
When energized, the solenoid blocks pressure from the charge air from reaching the WG, so the WG sees the pressure from the intake or atmosphere. The moment after the solenoid is energized, any air pressure on the wastegate blows back out to the intake/atmosphere, relieving any air pressure on the wastegate.
Downsides: If the solenoid fails in the energized position, your wastegate will NOT open. However, the same general risk is present in a bleed setup. If it somehow fails in the energized position, it will bleed as much air as the stock restrictor will allow, but never absolutely stop pressure from getting to the WG. Failure in the energized state of either setup will cause massive overboost problems.
