Here's a thought, I'm sure it's a no brainer, but have you checked the fuel lines for leaks through the entire length, say near the tank or at the fuel rail? Possibly at the Fuel Filter? I've also seen clogged fuel filters also than can create a weird suction effect after the engine is shut off continuing fuel flow after engine shut off, but usually that would result in a flooded engine. How about gas tank rust? Any possible rust holes? Anyway, just a thought. Occam's Razor is often right. "one should not make more assumptions than the minimum needed" If the engine is operating properly, perhaps it is somewhere in the fuel delivery or storage that is causing your fuel loss.

Just my 2 cents which I'm sure or worth less than that. <img src="/forums/images/graemlins/ignore.gif" alt="" />