Priming live hydraulic system on 400

If the pump has been apart make sure u used plenty of assembly lube, if you didnt, take it back apart and lube it, not worth ruining the pump from lack of initial lube. If the pump has been sitting dry for some time (like years), I would defintiely pressurize the resevoir, probably while cranking the engine a bit to get the pump going (unhook the coil power wire or something).

I do it differently and I believe it is the way the manufacturer intended.

At the top of the pump, you will see a little bleeder ball that is held in place with a concealed spring. Both the Pesco and Thompson pumps have it. Hold that down for a few minutes with the engine off. If that doesn't work, make something that will move the ball and place a heavy weight on it. Let it sit overnight or until oil leaks out.