I have noticed the last two times I have put fuel in my truck that when I un-screw the fuel cap it hisses and sounds like a soda bottle when you open it. Why would this happen? My father told me he thinks that my fuel cap is bad and not venting. I have also noticed that my fuel pressure is a little low I believe. It bounces at idle between 10-14psi. I do have a snubber installed on my gauge as well. Also can anyone tell me what the stock fuel pressure is for a 12valve?

Mine does the same thing. Only happens if you drive it and turn it off and instantly take the cap off the tank. Doesn't seem to operate any different so who knows, maybe it needs some pressure to help the lift pump. Fuel pressure is around 17-20psi at idle and shouldn't drop under 25psi under a load. 25-35psi is typical.

Clogged tank vent? Almost is a common problem. Read my sig below.

ISX- mine does the same thing. Only happens when you run the truck then turn it off and open the cap right away. So I'm guessing that is normal and not harmful? Also I installed a Larry B's adjustable over flow valve. I installed it and had to turn the adjustment in a good bit but I now have roughly 17-20 psi at idle. The truck actually feel like it drives and pulls smoother. I would guess this is because it was starving for fuel up top dude to low pressure.JAG1- do you have any pictures of you tank vent setup?

Being its a 12V there isn't any way for compression gases to get back to the fuel tank. Like on the 24V since the injectors are in the top of the head and the return rail is part of the head you could have combustion gases leak back into the return rail from a bad copper shim. But this isn't possible on a 12V.

A clogged tank vent will cause suction, not try to blow the cap into your hand when you open it. Can you tell if it's vacuum or if it's pressure build up?

It probably needs a new fuelcap

I have a new cap in mine and it has a ton of suction now. My tank has always been a little collapsed in on the bottom but its really bad now and I can hear it rounding back out when I remove the cap.

Check your tank vent on the fuel sender...

Is the vent the one on the far left of this pic? http://www.dieseltruckresource.com/dev/fuel-tank-pickup-tube-t128527.html

I have a new cap in mine and it has a ton of suction now. My tank has always been a little collapsed in on the bottom but its really bad now and I can hear it rounding back out when I remove the cap.

I read about a guy, on another forum, that had the same issue. Bought something like 3 different brands of vented caps and tested them. He found the best one was the Stant and the Napa brand did not vent at all. His buddy tested them down at his smog station diagnose equipment. One guy on this thread said his tank collapsed so bad it cracked. Yes, the vent is the one on the far left top of the tank. I do not trust these Dodge tank vents because once when I topped off my tank that vent continued to spew out a stream of diesel fuel that didn't stop for about 6 or 7 minutes. So mine failed to hold the fuel in. I eventually just blocked it off for good. I forgot to say...... I could get away with blocking my tank vent because I already had another vent mod of my own installed.

Clean your vent and add some plastic tubing to the barb. 2003 Ram Cummins NV5600 with gauges and a Smarty! Not much more.Sent from my iPhone using Tapatalk

My vent has a small plug over it. I pulled it off yesterday but it didn't let the pressure off. Stopped at auto zone today and picked up a "vented" cap but it does not vent either.