2001 Chevy 2500HD 8.1. I have no real pressure at the schrader vale on the fuel rail. If I dump gas into the throttle body the truck will run for 4-5 seconds then die. I have replaced the camshaft position sensor and the crankshaft position sensor was replaced a few years ago. I have also replaced the fuel pump 2 1/2 years ago although it was a cheaper fuel pump I bought online. Could it be the fuel regulator or most likely the cheap fuel pump?

SOURCE: '88 chevy truck, no spray from injectors

Not sure on that model what controls the injector pulse, but most vehicles either use the signal from the crankshaft position sensor or a cam position sensor. You should use a LED testlight, (NOT A BULB TESTLIGHT!!) and backprobe the injector terminals (with the other lead of the testlight to ground) while cranking the engine over. If the light flashes on one of the terminals, then you are getting injector pulse, and the fault lies elsewhere. If not, then you will need to replace whatver sensor is used to provide engine position signal on that model. Also, check the wiring to that sensor. Some vehicles have problems with the crankshaft pulley harmonic balancer failing and damaging either the body of the crank position sensor or its wiring.

SOURCE: 2000 chevy blazer, truck cranks

Does your battery go dead?

SOURCE: 1999 chevy blazer wont start

THE FUEL PUMP IS BAD.

if your losing fuel pressure after the pump runs the drain back valve in the pump has failed.

and i doubt that you are seeing enough fuel pressure to run a vortec engine.

low fuel pressure equals a non running vortec

SOURCE: I own a 2000 chevy blazer with a 4.3 v6 vortec. It

did you check power and ground at the fuel pump connector?there should be power at two wires at the connector,one should have constant power with the key on and thats for your fuel gage,the other power wire should have it only when cranking or for about 3-5 seconds when the key is turned on,check both of those first and that will let you know that everything is fine all the way forward of that connector,also did u replace just the pump or the whole sending unit?if you just replaced the pump the connector that runs fron the sending unit to the actual pump itself inside the tank also goes bad on this setup too,look for brown or burn marks on the inside of the sending unit where this connector hooks uo,hope this helps

SOURCE: 1999 chevy blazer fuel pump cycles when key is on

check or replace fuel pump relay