The way the game calculates fuel consumption with a 1/AU is wonky. Flying a Volk Frigate, upgrade to a Longhaul engine, which should provide 1 fuel per AU efficiency. What I notice is the engine actually consumes 2 fuel per AU, stopping consumption at some point with no rhyme or reason I can detect.
Okay, but my crew is level ~20, ship stats at 250-300%. Even in the absence of any rumors and all saves passed, over several years of game time, I have never once seen the fuel achieve 1/AU over a long trip. What sometimes does happen is the fuel counts down for a while, then stops entirely when near the destination, so no fuel is consumed during the last few AU of the trip, or short jags where it counts 2 fuel for 2 AU (which is the promised 1/AU), then skips back to 2/AU. But for long trips I've never got 1/AU, no matter what. Should that be happening?
To be clear, there was a bug with fuel consumption that allowed 0 fuel travel but we reverted to the original code, no change. The fuel consumption rules are the same for the last 3 years.
Let me clear up a few points of confusion.
1. This is not a new bug or change, these are the fuel consumption rules. 2. Fuel/AU is reported as an integer (1) but are generally fractionally higher. 3. Travel events and rumors can increase fuel use, further expanding this fractional increase. 4. This has nothing to do with Longhaul engines, every engine type works this way -- big, small, chaser or Warhammer.