Air coming out of passenger side fuel tank.

I have a 2006 Volvo with the D12 engine. When the engine is running and I have the fuel cap off, I can feel air coming out of the fuel tank. This only happens on the passenger side tank, the drivers side has no air pushing out of it. I shined a flash light into the tank to see if I can see any air bubbles but I did not. Is this normal? Could this mean my injector cups are bad?

 

My truck runs great, 6.1 MPG, the coolant system doesn’t seem overpressurized since it’s not dumping coolant into the overflow and the coolant itself looks clean. How can I check for bubbles in the return line? I shined my flashlight into the fuel tanks and I see no bubbles while the engine is running. There’s not a whole lot to see while looking into the fuel filler cap hole on the fuel tanks but I do see a tube and it’s not bubbling out of there. I’m not sure I’m I’m looking at the fuel return line or if that’s the one that sucks the fuel. If it means anything the fuel water separator clear bowl is almost empty, only a little bit of fluid on the bottom. I’m not sure if that’s good or bad.

I would just ignore this but im having some starting issues. What’s happening when I try to start the engine when warm or cold after sitting for about 20 minutes is a long cranking time and I have to press the throttle to get the engine fired up, but after it starts it runs perfect. I’m kinda leaning away from thinking it’s injector cups becasue of that. Is there any kind of fuel check value on the system that might not be holding pressure while the engine is off?