Attempt at test running a Magnum

Professor Fate said
You say you've got it hooked to a '92 B250 fuel tank- is that the tank that was original to your engine? If not, that could be your problem.
'92 was an odd year, as the TBI LA318 was replaced by the 5.2 Magnum, but the TBI LA 360 was still being used and would not be replaced by the 5.9 Magnum until the following year in '93. Therefore, there were two different tank/pumps being used in '92 depending on which engine was ordered- the TBI system required about 14 1/2psi., while the Magnums with MPFI needed 55-60 lbs. IIRC. So, if you're trying to run your Magnum off of a TBI tank & pump, you won't have sufficient pressure for it to operate.

I swapped a 5.9 Magnum in the place of my ‘91 318 TBI motor in my Dakota and used the same pump and tank. I checked the part numbers and they interchanged. The pump doesn’t have the FPR on it so pressure is controlled at the rail or TBI, and adjusted accordingly.

There are issues though depending on what year PCM as they went to a returnless style system and had a FPR on the pump. My 5.9 PCM is from that era, so I just made sure the static pressure matched and left the vacuum hose disconnected so pressure was constant like the PCM expected.