I know this is likely but I'm at my wits end with my gf's Blazer. I'm used to working on Fords and Jeeps where there are very few things that would keep them from running. With this it seems there are just too many for sane people.

Here's what I know about said Blazer:

It's 2000 2 door 2WD. She had it about 9 months before it just stopped like it ran out of gas. This was fairly common as the fuel gauge didn't work. They had someone put in a new pump assembly and it still won't start. The pump will not run. She doesn't have the resistor key and the security light goes off but the pump just won't come on. Fuses and relays are good. It will run if you bottle feed it but the fuel pump never turns on. Tested voltage at the relay pins and got nothing from all 4 holes. So I thought it was the security system and left the key on for 15 mins. Got power but when I put in the relay, nothing. Still no pump. The vehicle won't run if you don't have the relay and fuse in place.

Please enlighten me on what connections I should clean or parts to replace because the number of things that have to be right for this thing to run are astounding to me.

 

Could be the security system. But I have to ask - do you know what brand/make of pump was it replaced with? If it wasn't a AC Delco or Delphi brand that could still be the issue. These vehicles are super picky about electrical things like cap, plugs, rotor, pumps etc.
Try searching in here for 'cranks but won't start'. You may very well find the answer you need.
Also search for 'passlock' security, etc.
Sorry I'm not up on these security issues, but I hope I can lead you in the right direction to an answer.
Priming the throttle body & it runs does = no fuel... bigger question is why.
Try checking out https://blazerforum.com/forum/2nd-ge...problem-42968/ &
https://blazerforum.com/forum/tech-a...agnosis-23038/

 

I'll have to check to see who made the pump. I thought that if the key didn't have the resistor sticking out of the top end that it didn't have the goofy pass lock system. I tried the old pump by just giving it power and it spun but not sure how much PSI it would make. Will go through the diagnostics for that next time I'm down there. But even if the pass lock system is angry, couldn't I manually jump the pump to start just to make sure it's even going to make pressure? The line hasn't got a bit of pressure in it since the install.