Engine/Transmission (1998.5 - 2002) excess pressure in fuel tank

[GW01]

has anyone had this problem. after shutting down my 99 3500 dually cummins,i heard a hissing sound comming from under the bed near the fuel tank. i checked the area and did not find any leaks but the noise continued. i opened the fuel cap an the excess pressure came out of the tank. i guess the noise was from the excess pressure. the outside temp was around 40 degrees so i do not think that expansion would cause the problem. this is the first time i have heard this noise. thanks

 

[DRAG DIESEL]

The one time I was arround someone when this happened it was because of exessive returning of fuel to the tank via the return line from the injectors... . or



it could be a bad cap... . i think they are designed to vent a little... ... best of luck to you.

 

[rashwor]

I am willing to bet that the vent on the tank is stopped up and what you were hearing was the tank trying to suck air (vaccum) through the vent. Been there done that. The vent is on top of the tank where the fuel lines connect. The cap is non-vented. When you opened the cap, it sucked air in. This is what happened to me. It was a vaccum due to a stopped up vent, not pressure inside the tank.

 

[RustyJC]

What? No mention yet of the infamous red caplugs?



Rusty

 

[rashwor]

My bad Rusty...

I thought about it but did not mention it. The vent on the tank came from the factory on a few trucks with a red cap on it to prevent dirt from entering the tank. The red cap was supposed to be removed from the tank before assembly, but was not removed in all cases.



You can check and see, but I am still betting the vent is stopped up with mud and dirt. This happens to mine regularly.



How is that Rusty?

 

[propuller]

I had the same thing happen on my 98 the tank was actually being crushed due to the vacum & the lift pump was shot. I put on a new lift pump & when i pulled the fuel cap off a loud hiss or a rush of air could be heard this was from the tank being sucked flat. you could see the dents in the side of the tank from the vacum. I pulled the tank & there it was a bright red cap on the vent port that somebody from the factory forgot to remove. . Good luck.



Kurt

 

[HEMI®Dart]

more info: http://www.dodgeram.org/tech/dsl/ISB/low_power.htm

 

[JR2]

If in fact your tank is under vaccume I would think that your lift pump would be shot in a short time... time to check your fuel pressure once you find the problem.