I can't give you a definitive answer, but I know from night to morning the pressure is gone. Judging by my experience it seems like a few hours (3-4) would do the trick, but that's only an estimate.
Is that with a mechanical or electric fuel pressure gauge?
Good question.
I think he means in general. You can basically do two things if you want to work on the fuel system but don't want to deal with pressure:
1 - Let the car sit over night, it will be gone by then
2 - While the car is idling, kill it by triggering the inertia switch in the trunk. This is will cut off the fuel pump and there will be no fuel pressure. The car will stall out and a CE light will come on, but, after you are done and enable the switch and start it up, it should go off. This is how I always do my fuel system work.
Adam
Al, that's normal. The system is designed to not hold pressure indefinitely (there's no reason to). Otherwise a more robust check valve would have been used and the prime-out could be omitted.
When people post, they should note if they have aftermarket FPR's since they almost always lose pressure very quickly after shutdown.
If you know the gauge is good and have checked that it's not the FPR that's causing the loss of pressure (one can carefully use a pair of fuel-injection hose clamps on the return side to see if pressure shuttles back up), then the pump is the reasonable option left.
To be sure you could open the delivery side and do a volume test.
Good luck.
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