Dear all,

I was reading some old posts for a intake vacuum leak my car have and read an old post about vacuum build-up in the fuel tank (shogun and Russel).

I was curious about the activated carbon canister and fuel tank breather valve, learned they're parts to consider replacing on older cars like mine. I recently had my fuel pump sending assembly, fuel pressure regulator and fuel filter replaced.

I just noticed I definitively have a vacuum forming in the fuel tank, as today I drove 30 miles or so and when I stopped the car, opened fuel cap and heard a clear hissing sound for 3-4 secs before it achieved outside atmospheric pressure.

Should I be concerned with this? I don't want my fuel tank to collapse or bust my new fuel pump!

Is this a sign of a problem with the fuel tank breather valve, or carbon canister, or expansion tank or ???

How could I make sure what is faulty?

Thanks for your advices!
Alex