1999 Chevy Silverdo cranks but wont start

Question edited for clarity and fix typo.
Question moved to model category.

'Cranking' is purely the engine turning over. It cranks, almost starts and then it does nothing next time you turn the key? Flat battery.

Or, you turn the key, it cranks, fires and almost starts and then dies? More reasons for that scenario. Check for diagnostic trouble codes. Did you disconnect the battery when you replaced the fuel pump? Did it work after that? Does it have an engine immobilizer and did you reset it after the disconnect?

https://www.google.com/search?q=1999+Chevy+Blazer+crank+no+start

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could be fuel pump or even crank or cam , timing sensor. Did it start running strange before this?

First key on you should hear pump run a couple seconds if you think it's the pump have someone crank it over and another pound on the fuel tank this sometimes makes the pump motor start to run, if it does that may be enough for you to drive to a shop for a new fuel pump.

if it is fuel injected that truck needs in the range of 70-80 psi to run
had one with 45psi that would not run so make sure it's putting out enough psi

next time it dies, cranks and wont start, do this if you have someone else with you. carry a spare spark plug, then when the problem arises pull off a plug wire put the spare plug into it and ground the end somewhere in the engine bay, then have someone bump the key and watch to see if the plug has a spark or not, that will at least tell you what problem to go searching for. if it had air, it still does when it dies so it will either be spark or fuel related. just because the pump runs, doesnt mean the ecu is telling the injectors to fire, so still could be a fuel issue. is the check engine light on?

i had that problem with my car but i had a key with a chip in it and one with no chip. i kept using the one with no chip and my car was dieing. as soon as i used the one with a chip in it my car started right up and stayed running.

try to start it a few times then go smell your tail pipe if it smells like gas you converter is stoped up!

try the spare key and see what happens ,if no spare then call out a auto locksmith and have one made and the keys reprogrammed but it scould be you lost the chip out of the key or its been wiped by a mobile phone or a TV screen even a body scanner or any electrical field

you need to put a scanner on it and see what code comes up.
my guess would be the crank sensor which is very common .

are you using the original key for the car because it sounds like a theft system problem I had a 2000 jeep that did the same thing it would start for a bit and then quit on me found out that the key has a chip in it so the key i got cut works for the lockes but cant use to run the car