I don't understand how you can be using a pressure gauge (PSI) to read vacuum, unless you have one that reads in negative numbers. Vacuum should be read in Inches/HG (Mercury), which is something like a barometer (milibars)
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.