Hi guys can anyone (veeeight) tell me why when I remove my fuel cap to refill i get a sudden burst of pressure releasing past the cap when i loosen it off. Is this normal?
Normal.
Modern fuel systems are predominantly sealed systems, fumes aren't supposed to be released to the atmosphere, so in most cases the vapours get channeled to the EVAP charcoal canister. Then these get used when the car is in motion.
Most of the time the system will run at less than atmospheric, so the hissing noise will indicate a vacuum in the tank, but on occasion (depending on external ambient temperature, pressure etc) it can be under positive pressure, but this is rarer.
(Not all parts of the fuel system is under pressure, just the fuel rail and injector system is under high pressure. The rest of the system is "pumped" as opposed to "high pressure")
Yeah did it on me the other day, went from a 100% full tank right down to a red light on the dash and a 35 mile range. When I opened the cap I got the whoosh sound.yes this is normal and you will find it does it more when empty...