Try it without the fuel pressure gauge. If the car straightens out, then you know there was something wrong with the gauge installation causing the problem.

Otherwise, it could be a bad or restricted fuel pump...some crud could have moved from the old line into the pump causing a restriction.

Check your oil...does it look like or smell like gasoline in it? If so, the fuel pump diaphragm could have ruptured allowing gas to dump into the crankcase. The worst case could be a worn lobe on the camshaft that the fuel pump lever impinges against.

Hopefully it's something simple. Start with the simple and progress from there.

The problem was there before I did the work... That is why I  put the new hose and gage on, I have also tested with a hand held gage. The engine is fresh with only 400 miles on it, no gas in the oil and a new cam was installed during the rebuild.....

One thing I've been reading a lot about recently is modern grade motor oils no longer having the additives needed for engines with flat tappet rocker assemblies. Allegedly the lack of the proper additive package for older engines that have been rebuilt or new crate engines with flat tappets is resulting in a large increase in camshaft failures, within a thousand miles in many cases. The lack of the appropriate additives in the oil is resulting in cams not breaking in properly and failing. The probelm seems to worse in camshafts made from imported blanks than in domestically produced cam blanks.

There's a specific GM additive available at dealers to handle this break-in problem. Supposedly the cam lube that manufacurers supply isn't enough.

Whether this could be your problem I have no idea...that the fuel pump lobe on the cam maybe wiped. I just want to bring this up as a possibility since your having a newly refreshed engine rang a bell with me after reading these reports.

The simplest thing could be a bad fuel pump...maybe even installed incorrectly. You can try a new pump...I would try that first.

The problem with an electric fuel pump is it has to be mounted back by the gas tank for best performance and shielded so it doesn't interfere in your radio. Not much of a problem, but more involved than simply installing another mechanical fuel pump.

Hope you get your problem sorted out quickly and simply.

Thanks for the input... The engine builder is well known in the Northwest, he also races professionally with a big block Vette and a Chevelle. I trust that he put in the correct good parts and he was very specfic on the oil I used as well as the break-in method. But, anything can happen.... I ordered a new stock pump and I will see how that works..

C3454Vette