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New fuel pump, new injectors, pressure regulator holds a vacuum. What else could be bleeding off fuel pressure while it sits?
 

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Can you close off the return pipe?

That might help you isolate where to look.
 

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I guess I can. Not sure how though.
use a set of hose pinch pliers on the rubber return line right after the regulator, connect pressure tester, build pressure on fuel line by priming fuel pump. monitor static pressure. this will help diagnose if fuel pressure regulator leaks or fuel rail leaks including new injectors.
if all pressures remain steady, inspect steel return line for leaks (even wetness over rust is a leak repair as needed).

if all is well so far, suspect defective new fuel pump check valve.

PS do not use needle nose vise grips, they always allow leak. use proper hose pinchers.
 

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I get this same problem on my 1977 2.25 with a weber 34ICH.
There is no return line on these, any ideas?
 

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I get this same problem on my 1977 2.25 with a weber 34ICH.
There is no return line on these, any ideas?
totally different animals and set up, a 77 2.25 carbureted versus a 94 fuel injected V8. too many variables on your vehicle to offer a simple solution. Campbel has been chasing this issue for a while on the forum.

defective fuel pump, dirty fuel filter, improper fuel bowl level, improper timing, worn out or improperly gapped ignition points , fouled spark plugs, dirty cap and rotor, worn out/low compression engine. are some concerns which need to be researched in order to make your engine a well tuned machine.
even then a cold carbureted engine needs choke and priming on a first start, fuel injection uses high pressure electric fuel pump and pressure regulator to build and maintain proper constant fuel pressure. ECU's to control injector pulse air meter throtle position etc. again very different animals.
 
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