Fuel system for vehicles

[theHolyCow]

edit:
Isn't it possible to freeze a car with TogglePlayerControllable(playerid,moveable);? Just execute this command when a player enters a car, so he won't be able to move. He can, however execute commands. If he wants to leave the car: /leavecar; If he wants to teleport to a fuelstation: /fuelstation for example. If a player uses /leavecar, just throw him out of his car, and unfreeze him with said command.
When he teleports in his car-without-fuel to a fuelstation, and buys fuel so the amount of fuel is >0, he can also be unfrozen, but don't throw him out of his car

Is this possible?

Yeah, I think it is. I am currently busy with exams, when I've time I'll see if I can make something out of it.