[klhansen]

Did you poke a wire thru the connection on the turbo wye? Maybe it's clogged. If so, it wouldn't let pressure get to the MAP sensor (or your boost gauge). But the gauge showing -5 psi with the engine off is an indication that it may be a problem with the gauge. That wouldn't cause a code though.

 

[klhansen]

Where the hose connects to the turbo wire.

 

[klhansen]

Im sorry man, what exactly is the turbo wire?

Damn spell check

TURBO WYE is what I meant to type. The hose that connects to the MAP sensor over on the heater box runs down to the front of the TURBO WYE and connects to a metal nipple on the front of the wye (can't really see it in your pic).

 

[klhansen]

YES!!
Sorry it took so long to get that point across. I was just getting ready to post your first pic with an arrow pointing at it.

 

[klhansen]

If the lines are clear, a bad MAP sensor could cause a low boost code, but not actual low boost. But the gauge should show some movement, assuming your turbo is working correctly (not bound up) and the intercooler boots aren't leaking severely. But the gauge may be bad as well (multiple issues?) if it doesn't move at all. If you have a mityvac tool, you could pull a vacuum on it and see if it moves. Or hook up a tire pump and put some pressure on the MAP sensor and see what the scan tool shows for pressure, as well as check the boost gauge. But like Nick said, that's a boost gauge for a gasser with a turbo, which develops vacuum as well as boost in the intake system.

 

[klhansen]

Check for a vacuum leak on the intake, the 7.3 's are known to suck air at the back of the intake.

Unless you're talking about a non-turbo 7.3, the intake "sucking air" won't reduce boost, as the only place a Powerstroke can suck air is on the intake side of the turbo, and all that might do is bypass unfiltered air into the engine. But anything leaking between the turbo and the intake plenums would cause a reduction in boost.