help with humming gas cap

[lloydcruz]

hi everybody,

im a noob here. hope you could help me out with my problem.

bought my first car early this month. it was a 1989 corolla (small body) 1.3L 2e engine. i noticed that my gas cap is humming when the engine is running (both idling and moving). when i turn off the engine it goes away after 2-3 seconds. i also tried removing the gas cap when the engine is running and i hear a gush of air. i'm just not sure if it is sucking or blowing air. after that the humming sound disappears.

a mechanic told me that it's the gas cap. but im also worried that my fuel tank breather (if my car has one) is blocked. i am also thinking that could it be the reason why my fuel mileage is not very good (approx. 5-7 km/L).

i really need your professional and experienced opinions.

thanks.

[macgyver1432000]

It's natural when you open your gas cap, there's a gush of air, like vacuum. The reason why your fuel consumption is high, it's because: Ignition timing is not correct; carburator not adjusted properly; spark plug gap and contact point gap is not correct.