Comment on the vacuum needed to move the Fuel.
I have no specific spec as this is sort of new territory for someone to investigate

However, the Fuel has a certain amount of weight (pulling the fuel up against gravity) as well as viscosity to it. Added to this is some resistance due to the long hoses and tubings going to the Fuel Tank.

The 5-6 Hgs does not seem unresonable when you think of the above.

If you hooked up the Mighty Vac at the Fuel Oulet of the Fuel Supply Pump; besides the stuff mentioned above you also have to create enough vacuum to overcome the pressure of the 2 little valve springs.

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84 300D, 82 Volvo 244Gl Diesel