2nd Gen Non-Engine/Transmission vacuum in fuel tank?

[Piersol]

I've read some posts about pulling a vacuum in the fuel tank. When I unscrew my cap (original) from my 1996, I get a little vacuum. Sort of a "fffft" sound. Does everyones do that or do I have a plugged vent. It runs fine.

 

[illflem]

They all hold a slight amount of vacuum and pressure. Usually when there is a problem it will collapse the fuel tank. The tank is vented by both the cap and a vent on the fuel module. On some years the vent caps were accidentally left on, this shows where and how to check http://dodgeram.org/tech/dsl/ISB/low_power.htm

 

[Cooker]

I chased this for a long time.



It could be the fuel cap. There is a sping in there and it is supposed to vent a little .



There was also a fuel vent cap on the top of the fuel tank module that may have been left on during production. This seemed to be more common on the newer truck. You can check ou the cap issue here: http://dodgeram.org/tech/dsl/ISB/low_power.htm



For me, I finally tracked it down to a Rollover Vavle (thanks to Evan A. Beck ). It is a valve on the top of the tank that is supposed to vent normally, but when the truck is rolled over it closes and does not allow fuel to escape out of it. If I remember correctly it was about a $25 fix and about 15 minutes of my time. All is well now.



Mine had created so much vaccume that it started pulling in the tank at the bottom, and not it appears to be dented.



The vaccume is not good because it will cause your lift pump/fuel system to work harder.



I can dig up the PN's and some pictures of of the parts if you would like.







Edit: I guess I took too long to type. Bill beat me to the vent cap.