Finally got around to installing a real boost gauge. It connects with a T into the master cylinder as has been discussed before. When idling or putting around the boost is actually negative. Drops to -0.5 and will ride between there and 0. When you step on it the gauge comes up like a charm. Much different from the factory gauge. Is the negative reading normal?

 

The line to the master cylinder is a vacuum line, which suppliers vacuum to the master cylinder when the throttle body plate is closed (off throttle), thus augmenting braking force (vacuum assisted braking).

But when your foot is on the gas, the manifold vacuum goes away. At steady throttle cruising you should see little if any manifold vacuum and a zero gauge reading. But stuff your foot into it and ramp up the turbo, boost will build and that line will see the manifold pressure.

 

Thanks Mark. Always helpful. I am seeing negative vacuum at idle on the gauge. I can only guess this is normal as it is a vacuum after all and you would expect it to pull something less than zero. As you say, once you put the foot in it I get up to 0.6 bar. Nothing more. I have a stock WG and spring. I thought I would get 0.8. Perhaps it is time for a rebuild.