Engine/Transmission (1998.5 - 2002) humming noise from fuel tank?

[VolsFan]

I dont mean to ask a dumb question, but on my 99, I have been hearing a humming noise coming from my fuel tank, been doing this for a few months now. It sounds like pressure built up, so I unscrew the fuel cap and can hear pressure escape, the noise goes away. If I stand outside of the truck for a few more minutes, the noise will come right back. This has been getting really annoying, especially when I'm standing outside of the truck talking to somebody, then its embarassing. Also, I've been noticing my fuel pressure is slightly lower than normal, hope this is somehow related. Any ideas of how to correct this? Thanks.

 

[JOdell]

Does your truck have the in tank fuel pump? I would guess that is what it is. I haven't hear my 01 do it, but I don't have the in tank kit. -Jason

 

[VolsFan]

No, i dont have the in tank fuel pump, never will get that, but i was talking to my dad about it earlier today, told me it might be the fuel cap. Maybe its not making a tight seal; allowing air to escape. Tomorrow i'll go out and get a new fuel cap for it and see if it corrects the problem, that would be too easy, but makes sense.

 

[WestTN]

It sounds like your vent is plugged.

 

[Thomas]

To add to WestTN's post, your tank should be open to the atmosphere through the rollover valve (as long as the truck is in an upright position!).

This is what is on the top of the tank: http://img170.imageshack.us/img170/9308/topoffuelmodulelr9.jpg

The OEM fuel filler cap is the same, gasoline or diesel (P/N 52102432AA CAP, Fuel Filler, w/Tether), and has valving to prevent excessive pressure or vacuum conditions, something not seen in a properly functioniong diesel-powered Ram.

If your noise is coming from the cap, your tank vent is likely plugged. If the noise is coming from the rollover valve, you probably need to R&R the rollover valve.

 

[obert]

mine does that alot, but I dont think it comes back after I remove the cap-- never really checked. Its never bothered me much, though, and honestly if it's only a little positive pressure (1 or 2 psi) I'll live with it in hopes of a little help keeping the carter happy.

In this case it is comming from the tank, not the cap.



However, am I mistaking this pressure noise for vaccum noise? If the tank isnt venting right it should draw a vaccum in the tank. I only have noticed this after a drive, shut down, and returned to the truck several min. s later to get somthing out of the truck. Figured it was a build up after fuel was no longer being drawn from the tank.