If you haven't visited it already, the 700/900FAQs on this site are a good resource for troubleshooting. For fuel issues:

https://www.brickboard.com/FAQ/700-900/FuelSystem.htm

"...I reinstall the fpr with the return off and no fuel is passing the regulator..."

So it sounds like the pump is providing fuel flow but not at the proper pressure. It needs to push fuel at at least around 50-55 psi, as the regulator will cut it down to 43.5 with no vacuum applied and 36.5 at idle and vacuum connected. A fuel pressure gauge is a handy item to have in your tool arsenal these days.

If you suspect a bum relay you can either a.)check for voltage back at the pink pump power wire with a volt meter while cranking the starter, b.run a hot lead straight from the + battery terminal to the pink wire, or c.)pull the pump relay and jump two of its sockets (I think pins 3 and 5 but I don't recall for sure). Maybe someone else knows. Also, the 700/900 cars are known for frying the connections in the relay board.

I'm wondering if you accidentally got a low pressure tank pump that the two-pump Bosch systems use vs the single high-pressure pump for Regina systems.
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