Forddude86

2000 with a 5.4 with engine running it reads about 30psi. With key on engine off, it spikes to 40 then drops to 0 within 5 seconds. I found this trying to hunt down an idle issue. It runs rough at idle but only sometimes. It happens more often when outside temp is cooler. I've heard maybe the fuel pressure regulator but any advice is greatly appreciated.

Tackle

It should hold pressure for a minute or two at least.
I'd agree with the fuel pressure regulator.

Forddude86

Is the regulator integraded into the fuel rail on these? If not, where is it?

Tackle

Driver side by the egr. Has a vacuum tube attached to it. It is held on by a snap ring.

Forddude86

How do I test it? I also heard about some fuel pressure regulator bypass valve and a check valve on the fuel pump also being possible causes.

TRD-Toy

You need to install a block off at the fuel return line at the fuel rail. Pressurize and see if system holds. If it does. Check the regulator vacuum hose or oring that is inside the rail. I doubt your lose that much pressure that quick in the vacuum hose. Bet it won't hold because the fuel pump. I'd dead head the fuel system at the fuel filter. Pressure line right to the gauge set. Pressure will be higher than 40 psi deadheaded to begin with. Should still hold for some time.

Forddude86

Follow-up: replaced fuel pressure regulator and the pressure issue was fixed. Thanks for all the help.