Thanks, Bob
    I did a supply test before dropping the wbx engine, and remember the
volume was a bit low, but not a lot. Fuel pressure static and at idle is
ok right now. But the pump is definitely cavitating: I can see the pump
spray air bubbles around the white plastic pre-pump filter, can hear the
air bubbles pass through the pump in bursts, and can hear and feel them
when I squeeze the return line with my fingers. I replaced the main filter
about 1,000 miles ago and the prepump filter today. No difference. Air in
the lines seems like it matches the running problems too--surging at all
speeds, misses, sudden coughs, etc. Finally, when I took the supply line
off the tank nipple I had the filler cap off and the gas dribbled out way,
way less than I would expect it to move out of a hole that size in the
bottom of a container.
   I heard that '87 up vanagons didn't have the pre-pump filter. True?
Could VW have stopped using it because it restricted flow into the pump?

            Thanks, Sam