Fuel pressure question

I have a 94 K1500 with a 5.7. I checked my fuel pressure the other day, when I cycle the key I have 21 psi but as soon as the pump shuts off the pressure drops off to zero in under 10 seconds. i did notice a very small drip from the injector when pressurized so I replaced the o-rings on the injectors and I also replaced the PR diaphragm. Tested it again & drip is fixed but pressure still drops off when the pump shuts off. I have checked all over this truck but I do not see (or smell) a leak anywhere. The pump will maintain pressure with the engine running. I replaced the fuel pump & sending unit about a month ago...installed an AC Delco pump, EP377. So my thoughts are:
1) Bad fuel pump? I assume there is a check valve in the pump?
2) Leaking off inside the tank (I didn't splurge on the sending unit...I think it is a Spectrum).
3) Do I need a heavy duty pressure reg diaphragm for the higher fuel pressure? The one I put in is just your standard rebuild diaphragm?
4) Bad fuel metering body or cover (injector pod)?

I don't want to pull the tank again if I don't have too but that's the way i am leaning. Any thoughts? Thx.

Ok...I took the pressure line off the TB, capped it and cycled the pump, the pressure spiked and pretty much held after the pump shut off. So, the problem is definitely in the fuel metering body somewhere.

Can anyone tell me...does a TBI I need a "heavy duty" Jet pressure reg, diaphragm for the higher pressure I'm running? Or do I have a bad fuel metering body? What else would make this leak off internally?

As long as pressure is maintained while running don't worry about it. Lack of fuel pressure when the engine is not running is not an issue...

I agree. The engine doesn't need fuel when it's not running.

yeah...I just thought the system was supposed to maintain pressure after the pump shuts off. And if it should and can't, where is it leaking off at and is it possibly creating a lean condition under heavy load driving (when I can't see the gauge)? I'm obviously overthinking this...I have a tendency to do that. Thanks for the opinion guys.

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Originally Posted by dispoejoe95

yeah...I just thought the system was supposed to maintain pressure after the pump shuts off. And if it should and can't, where is it leaking off at and is it possibly creating a lean condition under heavy load driving (when I can't see the gauge)? I'm obviously overthinking this...I have a tendency to do that. Thanks for the opinion guys.

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The fuel meter has a small hole drilled in it to bleed off fuel vapors.

Where does that small hole vent to? The outside air or the return line?

The small bleed hole goes to the return.

Quote:

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Originally Posted by sturgillbd

The small bleed hole goes to the return.

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Duh lol...moment of retardedness.

To the OP - FYI I have a fuel pressure gauge 2" before the TBI and when the motor is shut off it reads zero.