Vehicle in question is a 2000 GMC Sierra with the 5.3. If the truck sits for a little while, it takes a second or two longer of cranking before its starts, and then bogs for a second, and then continues running fine. If you turn the truck off, then immediately crank it again, it will start with no problem, and again, drives completely fine.

I just went and put a pressure gauge on the fuel line to see what its doing. Turn the key to the run position and pressure instantly jumps up to what looked like ~50 psi (hard to see from in the cab), but quickly starts falling even if the key remains in the run position. When I turn the truck on it hold almost dead straight at 50 psi, and barely makes a drop in pressure with a rev.

Now I know that the regulators have been a problem on these trucks since almost forever, but nothing it did screams at me that the regulator is failing, and at about $50, not exactly something I want to blindly throw at the truck.

I pulled the vacuum line on the regulator and there was no gas in it, which from what Im reading around, is a sure sign its bad, but nowhere have a read that just because there isnt gas in it, that it is good.

If the pressure drops off that quickly, then its most likely not the injectors right?

 

whats the status on the fuel filter?

 

Needs a change Im sure. The reason Im not attributing it to the filter is because the system does get pressure instantly at the turn of the key, and it runs completely fine once its going, it just wont hold the pressure when the pump isnt on.

 

bump

 

The LSx series of engines typically run with 58psi fuel pressure... don't know about your truck. If you are only getting 50psi with key on and it drops quickly, it may be a fuel pump problem. Appears the truck fuel system may be different than the F-Body LS1 fuel system, because the F-Body system is dead-ended and not vacuum compensated, with the regulator in the rear dumping the excess fuel back in the tank.