I don't know, I've never tested a fuel pump without the fuel pressure regulator in the circuit!!!

 

Reading the initial fuel rail test port pressure numbers you posted, this dead head pressure reading sounds similar, so perform the return line blow through test, to make sure its open back to the fuel tank & if so, as suggested, put the fuel pressure regulator on the suspect list.

 

Should the fuel pressure hold at certain PSI? The valve at the rail maybe no good, I may have to change the stem. I would think the pump is good.

 

How to perform the return line blow??Not quite sure what you said.

 

Disconnect the return line at the regulator, wipe it off, don't inhale while blowing into it to see if it's clogged. You might loosen the gas cap in case it's warm & the tank has positive pressure.

 

Yes the fuel pressure regulator should hold pressure for minutes after the engine is turned off.

See my previous post for KOEO & KOER pressure ranges.

The fuel pump isn't designed to try to pump into a dead head, so don't do that any more, it's hard on the pump.

If the return line from the pressure regulator back to the tank is restricted/collapsed/kinked/pinched, which the initial pressure readings suggest could be so, as it gave kinda like readings.

If you can blow through the return line ok, then it suggests the fuel pressure regulator has a problem.

 

"If you can blow through the return line ok, then it suggests the fuel pressure regulator has a problem."

Please explain your statement above. Do I use a compressor to blow air into the hole? If my regulator is good, I should not be able to blow air through the return line???

 

Loosen the fuel tank gas cap. Disconnect the return line at the fuel rail pressure regulator, wipe it off, don't inhale while blowing into the line with your mouth. If you can blow through the line it's open, if you can't, then it's obstructed somewhere, so trace it back to the tank looking for the kinds of problems listed above.

 

I revisited the fuel raid and re-connected my pressure gauge to it. The stem inside the raid valve is definitely no good. Anyway, at one time, I got 10 PSI with key ON. Now the valve has a little leak of fuel under pressure. The stem will not block fuel leaking out. I put a cap on it to block the leakage...

I think I need to fix the stem first ... can I change the stem or I have to change the whole valve?

 

I've never had a fuel rail Schrader valve problem, so I don't rightly know if the valve can be replaced, or if its designed for the whole fuel rail to be replaced.
Common sense suggests that like a tire valve, the fuel rail Schrader valve probably can be replaced, or it would be really expensive for a factory to have to throw the whole fuel rail assy away because a new Schrader valve was found to be bad right out of the box.

 

Do you think I have a leaking fuel injector, that's why I get no pressure on the fuel raid??? Just wonder ...

 

If the fuel rail test port Schrader valve is leaking, that's a problem.
If the drain back valve in the fuel pressure regulator is leaking, that's a problem.
If you have a fuel injector with a runny nose that's bad & you'd likely have a rich fuel trouble code & a really badly carbon fouled spark plug & the crank case oil on the dipstick would likely reek of fuel when sniffed.
If you have a clogged fuel return line, that's bad, as the fuel pump would be trying to pump into a dead head, kinda like the one you created when trying to test fuel pressure after the fuel filter with the T plugged.
Again test the return line to make sure it's open.

 

If the fuel rail test port Schrader valve is leaking, that's a problem. I use a plastic cap to block it for now.
If the drain back valve in the fuel pressure regulator is leaking, that's a problem. Regulator is new, highly unlikely it's bad.
If you have a fuel injector with a runny nose that's bad & you'd likely have a rich fuel trouble code & a really badly carbon fouled spark plug & the crank case oil on the dipstick would likely reek of fuel when sniffed. No fuel smell, no carbon found on plugs.
If you have a clogged fuel return line, that's bad, as the fuel pump would be trying to pump into a dead head, kinda like the one you created when trying to test fuel pressure after the fuel filter with the T plugged. If the return line is blocked, then the pressure gauge will show high PSI?
Again test the return line to make sure it's open.

 

If you'll check to see if the return line is blocked, we might know the answer to your last question.
Did this problem come about suddenly after some event, or slowly over time?

 

Update:

Finally, I got the fuel pressure gauge working after changing out the valve stem...

Here are the results:

1) KOEO, it read 40 PSI for 2 seconds and dropped gradually down to 0 PSI.
2) KOER, it read 30 PSI, step on the gas, 35 PSI. Once turned engine off, the pressure dropped gradually down to 0 PSI, it didn't hold the pressure at all.

Any idea? Thanks in advance.