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Hey:

I got a 5.0 that has been rebuilt. The usual rings, seals and what not. Anyhow I was just checking small simple things on my car today. Now I was checking my fuel pressure regulator and there isn’t any fuel that comes out of the vacuum line but when I plug the vacuum line with my finger the engine idles/runs a lot smoother, it doesn’t shake as much if you know what I mean. It also runs rich, you can smell raw fuel inside the cabin. Its stock other than CAI, BBK headers, E303 Cam and MAF conversion. What could be causing this? I will check vacuum and fuel pressure tomorrow night.
 

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Unpluggining the vacuum to the FPR bumps the fuel pressure to 40psi, if that fixes a problem with the car you may have a vacuum leak, clogged fuel injectors, too much timing, etc.

Lots of stuff is effected by dumping twice the recomended amount of fuel in the motor. rich running engines usually idle better than lean ones.

I would check for codes on the computer and the ignition timing first before chasing after a fuel related problem.
 

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The engine runs smoother when you plug the vacuum line to the FPR or when you plug the FPR where the line would be?

At idle, the vacuum line should be pulling roughly 18-20"HG, this keeps the check valve unseated allowing fuel to dump back into the tank through the return line resulting in lower fuel pressure. So as you step on it, you get less vacuum, check valve seats, and fuel pressure is allowed to build. I'm not sure what the pressure is supposed to be at idle, but there shouldn't be too much difference if idling with the vacuum line pulled, just more pressure.

If you're getting a raw gas smell, you might not have enough vacuum acting on the regulator diaphragm.
 
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