Vacuum reading for a 97 Crown Vic.

What should the vacuum reading be for a 97 Crown Vic when watching the vacuum reading on a ODB2 code scanner?
I am showing 9.8 - 10.2 at idle.

Since no one has been able to provide what I asked about the vacuum reading based on what the code scanner shows, can someone tell me what the vacuum reading should be right off of the manifold? For a 4.6 - 97 Crown Vic.

On a gauge teed into a manifold vacuum port, a healthy stock 4.6 at warm idle near sea level usually pulls somewhere around 17 to 21 inches of mercury, and the needle should sit steady. Expect a bit less at altitude, roughly an inch less per thousand feet.

The 9.8 to 10.2 on the scanner is probably not manifold vacuum. A 1997 4.6 meters air with a mass air flow sensor, not a manifold pressure sensor, so a generic scan tool's "vacuum" number is either calculated or a different value altogether. If your tool is actually showing absolute pressure, about 10 inches absolute works out to roughly 20 inches of vacuum at sea level, which would be normal.

Either way, a cheap vacuum gauge on the intake answers it for certain. A steady 17 or more at idle is good; a low or wandering needle points to a leak, a sticking valve or late timing.

Dana