This may have nothing to do with your case, but I had a similar issue once.
The issue turned out to be with my Default flight. I had created a cold start flight using a plane that had a three position fuel selector. When I saved the flight (making it the default flight), I had set this selector to the "Closed" position.
The plane I then had issue with did not have the same fuel selector options, and though I could physically move the fuel switch from "Off" to "On" it did not affect the software. In other words, it was still "Off."
To fix it, I started the default flight, turned on only the fuel selector, then changed to the new plane/flight. The fuel selector then worked properly in game.
Hope this helps!