Vaccume when removing fuel cap.

[Cooker]

I still have a suction noise when I remove my fuel cap. It seems to be more apparent after longer highway runs rather than cruising around town before I get fuel. I don't notice it every time I fuel up, but at least 2 out of 3 times.



I already checked for the red cap on the vent and the tank didn't have one. I then stuck a paper clip in the vent hole to see if it was plugged and it is not, at least until the 90 degree bend when the vent goes into the tank.



What else could be causing the tank to create vaccume?



Thanks for the help,

Ryan

 

[Thomas]

I believe there is a rollover valve in the tank vent system. I think the only way to pull a vacuum on the tank is to restrict the vent system—via a clog or a stuck rollover valve.

 

[Irontrader]

Cooker,



I know what you're talking about. I've noticed the same problem with mine especially when on long trips. I've got so any time I stop at a rest area I loosen the cap to reduce the vacuum.

 

[FDziurda]

Take a look at this link and see if this might be your problem.





http://dodgeram.org/tech/dsl/ISB/low_power.htm



Good Luck!



Frank

 

[illflem]

According to manual the fuel cap is also supposed to to vent both pressure and vacuum. I personally don't know how to check it but if it is working correctly I can't see how the vent on the tank module can make any difference. My tank makes a vacuum hiss when I open it also, always has, yet it runs fine, I wouldn't worry about it.

 

[Cooker]

Mine has since I bought the truck 20,000 miles ago. I can't say I am overly concerned about it, but it is one of those things I like to get to the bottom of. With all my luck I spend a Saturday afternoon to try and figure out the source only to come up with nothing. Maybe I won't worry about it anymore



One thing I didn't consider it maybe the noise is pressue building in the tank and not vaccume being created?



I have reason to belive that my return line may be obstructed (high fuel pressure numbers, and it's not the overflow valve), could that have anyting to do with pressure or vaccume in the tank?



Thanks again,

Ryan

 

[Alan Reagan]

Cooker, My 98 12V did it, especially after running on the big roads. For some reason, I thought it was pressure instead of vacuum when I would pull the cap. It wasn't excessive. I could just hear it bleed off when I removed the cap. I assumed the pressure was from the increase in temperature in the tank from unused fuel. Either way, the valve may be doing its job. The tank is not collpasing right. Has to be getting air from somewhere.