93' GMC sierra 2WD 1/2 ton 4.3L...Starting problems

[Mine999]

My friend has a GMC sierra as listed above. I am very familiar with the truck as I have helped him do almost all of the work done on it. The current issue is with it starting. We have gone through some trouble shooting and I would like to see if anyone else has some ideas on what we may have missed.
So upon removal of the air filter and housing to make the injectors visable on top of the throttle body, we have found that when "primed" the injectors fire once, then when trying to start the truck nothing. The stream of fuel seems to be without restriction or obstuction. After the first "prime" nothing. When trying to turn the engine over it seems like it wants to but no fuel come from the injectors.
What we have checked : The fuel pump initiates when the key is turned into the run position before trying to start. The fuel filter has been replaced. All of the connections from the relay, fuse, fuse box, etc are good (minus one detail that I will get to) Less a pressure tester, when "primed" it seems to have a significant amount of pressure all the way up to the fuel pressure regulator. We can hear the injectors clicking when primed. The fuel however has zero pressure when trying to turn the engine over. The wiring has been tampered with by the previous owner but seems to be up to standard when referencing the manual. The fuel pressure regulator has also been checked for any abnormalities, which to my eye has none.
Any input or ideas would be greatly appreciated.Thank you.

[pennermechanical]

Trying tO diagnose the same issue on a friends truck

[phipps]

Have you checked for spark at a plug as well as the coil?

Have you actually checked the fuel pressure?