Fuel system pronlems 2001 Tahoe 5.3 regular fuel

[dougefrsh]

2001 Tahoe 5.3L 183,000 miles. I have been experiencing fuel system issues.
First thing that happened was hard start and running rough. Mechanic pulled vacuum line on fuel pressure regulator and there was fuel on the vacuum side and he replaced regulator with OEM.
Couple days later I notice a sound under the hood and its coming from the new regulator/fuel rail. engine will also rarely start on the first try which was ALWAYS what it did. We changed out the regulator to a new OEM and still has the same issues.
I have also check fuel pressure and there is no pressure with the key in the on position and the fuel pressure drops to zero soon after shuutting down the engine. The running pressure with the vacuum line off is about 53# but the gauge is bouncing around quite a bit.
Fuel pump was changed out at 87,000 mi.
Once the truck is started, it runs fine and no check engine lights.
I am guessing fuel pump. Is there any way to know for sure that is the problem?

 

[dougefrsh]

I also changed out the fuel filter to OEM and no change.

 

[rockola1971]

Fuel pressure dropping to zero after shutoff and erratic fuel pressure readings already told you what is wrong. There is a fuel "leak". You have injector(s) hanging open (unlikely because "it runs fine and no check engine lights after started", fuel pump and/or its check valve is bad or leak in fuel line between pump and injector rail. When you are reading zero fuel pressure with key on, did you hear fuel pump even come on? Do that test!

 

[dougefrsh]

I listened to the fuel tank with the key on and no sound. Once I start the engine, I can hear the pump.
What is causing the vibration and chattering at the fuel rail?

 

[Fless]

The fuel pump comes on for only a couple of seconds when the ignition is switched "on." You may need to have someone cycle the switch while you listen down by the fuel tank.

 

[rockola1971]

I listened to the fuel tank with the key on and no sound. Once I start the engine, I can hear the pump.
What is causing the vibration and chattering at the fuel rail?

Vibration and chattering at the fuel rail is coming from your pump transmitted through the fuel line. Could be the pump itself making racket or your fuel pressure is surging up and down substantially. Me thinks your fuel pump is hosed.

 

[Donal]

This post does not apply to 2001 and later vehicles with one wire sending units.
Maybe a wire or harness connector problem.

 

[Fless]

Maybe a wire or harness connector problem. The oil pressure switch provides 12 volt to the pump once the engine has oil pressure. The pcm provides 12 volts to the pump (and many other circuits,) when the key is in on position. If you cannot hear the pump running for 10 seconds or so when the key to moved to run position, but once the oil pressure provides 12 volts supply, the pump and engine run normal, look for a reason for no volts to pump. If all else fails, remove connector from the oil pressure switch and install a jumper across the two outer pins in the connector. The pump shuld run imediately and continue to run until the jumper is removed. You can use the jumper to run the pump for the pressure tests as well.
If the vehicle has other circuites that should be energized with the key in the on position but are not, the ignition switch may be the fault.

I thought that the oil pressure switch situation was only on the OBS models. Is it still true for a 2001 NBS?

 

[Donal]

I not sure of the change date. You are probably correct. I will delete the post.