So I went out to the garage yesterday morning, and hooked up a fuel pressure gauge to my new motor. I turned the key to prime the line, then turned the key back off. And the fuel pressure immediately began to drop. I clamped the return line with some vice grips and the pressure then held steady. So I'm thinking... bad fuel pressure regulator?
Because I was concerned, I left the gauge hooked to the motor. Later that afternoon, after I shut the car off, I noticed that the pressure was holding at 45 psi, that it wasnt bleeding down. Now what gives? What? it only bleeds down when it feels like it? I was all ready to replace the regulator, but now the pressure appears to be holding.

 

maybe a piece of dirt? my sons truck was having a problem starting and i checked FP few times. after the second time i checked it started right up, no more bleed down. who knows what was wrong, but i sure got lucky on that one. i like problems that fix theirself.

 

I think Ed nailed it (no surprise, eh?). You may have had some debris in the fuel tank, and a piece may have been lodged in the regulator disc/seat valve. The regulators are pretty much self-cleaning as long as there is adequate flow, and the debris may have been cleared out. There is a minor chance, however, that the disc or seat is damaged in an area, and the disc has rotated away from that area (for now). Granted, that isn't as likely, but is possible. Don't be completely surprised if the problem returns.

Given that all the fuel that is pumped by the fuel pump doesn't get used by the engine, the unsued portion is routed back to the tank. All of that fuel, however, is filtered as it leaves the pump. In this way, the fuel is constantly being filtered and returned, then mixed into the tank. This process of turning over the fuel load through a kidney-loop filtration cycle tends to keep the fuel relatively clean, but can also take a toll on the filter.

In either case, be it a failing regulator or just dirt, it would be a good excuse to change the fuel filter to maintain the cleanest fuel tank possible. They're supposed to be done every 30,000 miles, but unfortunately, people rarely do. In talking to Rich at Cruzin' Performance, they usually pay the price later.

 

Dirt is a definite possibility. Like I said, this is a brand new motor, it had run about 15 minutes at the point when I put the gauge on it. But the rails sat around in the garage for about 5 months, more than likely collecting a bit of crud. They looked clean...