At 23:02 11/17/2016, OlRivrRat wrote:
>What Density Altitude are You doing this Testing @ ~

It certainly won't affect the not-running reading, as the regulator
regulates to 2.5 bar over whatever the manifold pressure is.  I'm not
experienced with high-altitude operation, but I wouldn't expect
vacuum readings/manifold pressure to be greatly affected relative to
ambient pressure.  The gauge reference is ambient, of course.

To get an absolute reading of output pressure as seen by the fuel
injectors, which is where the rubber meets the road, place the gauge
in a strong sealed box and tee the box into the vacuum line going to
the fuel pressure regulator.  Reading should be  a constant 2.5 bar
regardless of engine state.

Yrs,
d