Hmm that's a good theory... I wonder if there's a practical way of testing it short of installing some sort of clear fixture or peephole into the system.

I don't have a line running into my compartment, much too dangerous. The gauge is under the hood.

As for how quickly pressure drops, I need to take a better look at that. Once when I tried it, pressure began dropping at the rate of almost 10psi a minute, from its 30psi mark during idle. But that only happened once, probably due to a slight leak. The rest of the times, it drops relatively slowly, so slow in fact that I don't see the needle moving if I stand there for a minute or two.

However, I will definitely check this again tomorrow for accuracy's sake. I'll start the car and leave it running for a good few minutes, then shut it off and see what happens.

edit: However, if there were pressure in the fuel system and there were a leak somehow that caused air to replace the fuel in the line, I would have to suppose that that would mean the fuel tank was pressurized as well. I'll try opening the gas cap at some point and see what happens to the gauge.
--
Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'