Vacuum in Fuel Tank
I started to notice this problem when driving. My fuel gauge goes down from full to empty in a matter of 15 minutes. First I thought it was the level sender problem, but to my shock was the top of the fuel tank had collapsed, pushing the sender arm downwards. When I stopped the car, everything goes back to normal.
I discovered that there is some vacuum developed through the gas cap. If I close it tightly, then the problem will occur and my rpm is unstable. So from now on I leave the cap loose all the time, however at the expense of gas vapor escaping ang affects the fuel economy.
My mechanic told me that the EVAP purge valve is clogged. I hardly believe this, as I thought the valve's purpose is to release vapor from the tank, and not allowing any air sucking into it.
I'm reluctant to dismantle the whole fuel system at this point of time. The problem had permanently deformed the fuel tank.
Please.. any ideas is appreciated!