My 2001 OB just decided it won't start, after years of great reliability. No warning, I just walked out this morning and it acted like it was either out of gas, or a clogged fuel filter. The engine turns over, and as long as I pump the accelerator it sort of chugs along (maybe with an occasional misfire of some sort), but immediately stalls out when I stop pumping the gas. I just replaced the fuel filter so that's not it, and there's plenty of gas.

 

What else could suddenly go south on me to prevent starting, with no warning?

possible cap/o-ring problem on fuel pump.

 

http://www.subaruoutback.org/forums/110-gen-2-2000-2004/41182-symptoms-fuel-pump-o-ring-problem.html