Last week during some night currency, I noticed my vacuum gauge had dropped to zero and the DG had rolled over. I figured my engine driven pressure pump had died.
When I bought my F33A last July, it had just come out of annual and had 30 hours on a firewall forward overhaul. The vacuum gauge always read 3.5 psi (below the green arc), but the instruments always performed flawlessly. I figured the gauge was old.
The maintenance shop started looking into the issue and found the problem: the B-nut on the instrument air tube where it meets the firewall had backed off completely, preventing any of the pump air getting to the instruments (and gauge).
So, I flew around with an unsecured connection for approximately 100 hours before it became apparent.
Oh, the gauge now reads around 6.5 psi, near the top of the green arc.