My aftermarket boost gauge

i have a 1996 eclipse gst with a 16g turbo and i have a aftermarket boost gauge and the needle on the gauge is in the vac. side and it does not go in the psi side what does that mean

IF the gauge is correct, it means you have a dead turbo, giving no boost.

If it’s stuck in the VAC, then it’s probably a problem with the gauge itself, either it’s defective or it’s not hooked up right. Under normal acceleration, even in a non-turbo car, you should not be pulling vacuum.

Does it read 0 with then engine off, then go to the vac side with the engine on? Does it vary as you give it gas?

Here’s a good site with a demo:

The ONLY time you will see any boost is at WOT…At all other times, the throttle creates manifold vacuum… With a turbo, at WOT, the vacuum should drop to zero and then slowly build pressure as the turbo spins up…