Rep Power: 266

Why does my cap making a sucking sound sometimes, and sometimes there is no sucking sound? Isn't it always supposed to retain pressure? My fuel pressure test came out good, but I'm wondering if my cap is leaking sometimes.

 
Rep Power: 313

I notice mine makes the sucking sound more when I'm low on gas. If I have half a tank and I'm filling up it does not make that sound. I also find that the longer the gas sits in there (If I use less over a longer period of time) it causes more suction. I know this does not really answer your question, I just figure I'd tell you how mine seems to work.

 
Rep Power: 266

well I agree with that but this time when I was low on gas there was zero sucking sound, which is weird and not the first time it's happened.

 
Rep Power: 313

Maybe when you put the gas cap on, you didn't do it as tight as usual? I'm throwing stones here

 
Rep Power: 256

doesn't that throw a code if its not air tight i remember people failing emissions test for faulty gas caps.

 
Rep Power: 208

mine works the same as tbohar. i get a bigger sucking sound the lower i am on gas. it seems like this would be the norm. I always go 4 clicks tight after i fill up too. maybe that will make a difference.

 
Rep Power: 811

it depends on the evap purge cycle. every so often, the built up vapors get released into the engine to burn up. when you stop the car, sometimes you will have trapped vapors and other times you will not. its just luck i guess.

 
Rep Power: 266

There is a spring mechanism in the gas cap, what odes it do?

 
Rep Power: 266

To answer my own question, it must have to do with pressure in the tank when it's slushing around.

 
Rep Power: 313

Sweet, now you can rep yourself

 
Rep Power: 256

if i remember correctly i haven't had that suction sound in a very long time full or low tank what problems would that cause if there was a problem ???

 
Rep Power: 811

if there is a problem with the evap system (like a leak), the check engine light would come on right away. it could just be your car is working well burning all the vapors.

 
Rep Power: 256

ok yeah no check engine light so guess im good but i probably should change that filter it has never been changed going to look at your DIY.

 
Rep Power: 266

What filter, evap? What will it cause if it's clogged?

 
Rep Power: 811

evap filter usually doesnt need changing for 100k miles. it doesnt get as much use as a normal engine air filter. but if it gets clogged to the point where not enough air is drawn in, it may mess with the evap system purge cycle.

 
Rep Power: 266

It's amazing how much stuff isn't even mentioned like changing the fuel filter. Any way thanks for the info as usual gearbox.