I think just closing the vacuum hoses wouldn't give a very accurate restult due to effecting the EGR so much, and of what I can tell, the scangauge won't work with my car (not sure why).
Vehicle compatibility - ScanGauge MPG gauge - EcoModder.com
Also not on the list for UG
UltraGauge OBDII Compatibility
Only thing close I could do is read vacuum with and with out the mods driving at say 55mph with the idea of higher vacuum would result in better MPG.
If I could get instant fuel usage/MPG reading, I'm willing to test ideas. I live in the country and traffic is pretty low.
Also on the subject of diesel, the engine does not use a butterfly, so the engine does not have excess vacuum to use so it needs the vacuum pump to provide the vacuum.