On the early cars, there were two gas filling problem areas: Flexible lines in the tank it self that can move and block a one way surge flap in the filler neck, the second was the actuator that opens the same surge flap which could fail or blow out a fuse (E6), disabling the flap. There is a TSB for a Fuel Tank Hose Modification (dated 8-12-99) where: 1. Difficulty filling the fuel tank can occur if the flexible fuel hoses in the fuel tank obstruct the inner flap of the fuel filler neck. 2. Incorrect fuel gauge readings can also be caused by the flexible fuel hoses in the fuel tank, should they interfere with the travel of the fuel sending unit arm and/or float.
Couple of interesting reads:
http://www.renntech.org/forums/topic/2317-fuel-filling-problems-went-away/
http://www.renntech.org/forums/topic/5265-gas-wont-go-in-correctly/