If my ancient memory is still ok,
that's one of those years where Volvoes still had the system also sometimes used on BMWs and SAABs, in which there are two fuel pumps, one main pressure pump outside the tank, and another "pre-pump" (in SAAB vocabulary) in the tank, the second being there solely to deliver fuel to the main pump without the kinds of fluctuations which might be produced otherwise. On such cars, when the pre-pump dies, the car will run fine when it has more than half a tank of fuel, so that the main pump is supplied by siphoning action, but will die when the level in the tank drops low or when it all sloshed to one side in a corner.
This problem is much cussed and discussed at brickboard.com -- try shouting "Fy Fann!" at the car, too.