What's the status of the in-tank feed pump? Do you know if it's working?

To test it, remove Fuse 4, then jumper 12V from Fuse 6 to the OUTPUT contact for Fuse 4 (the contact farthest from the door). The tank pump should run as long as the jumper is in place.

Even if it runs, the short hose that connects the pump to the outlet pipe can be rotted. This hose is about 4" up from the tank bottom, so the problem (Main Pump sucking air) is more noticeable when the tank is less than half full.

If the '85 tank pump & hose haven't been serviced in living memory, that's where I'd start.
--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Sold 5/03)
'83 Turbo 245
'76 244 (lasted only 255,000 miles)
73 142 (98K)
'71 144 (track modified--crusher bound)
New 144 from '67 to '78
Used '62 122 from '63 to '67