1994 GCM Safari with the TBI on V6 engine. The

TBI can be very hard to diagnose and fix and even finding good parts.
no fuel pressure gauge in your shop?
you can not work EFI lacking such tools period
un less throwing parts is fund or cheap.

no country told at all, USA< IF I TELL YOU OUR FACTS AND YOUR NOT USA, THEN I JUST LIED TO YOU, WHY INVITE LIES.
36 YEARS AGO.
THE LAST ONE ALMOST RUNS. (love to see that)
a PICKUP car, I guess.
what engine is there now? displacement, 4 banger sure.
for sure not the diesel it is TBI gas (petrol)

an , A/B dual TBI injector, I see one, in a real shop manual

now the FSM engine page

• L16, L18 And L20b Engines
• Sd22 And Sd25 Engines
• Vg30i Engines
• Z20, Z22, Z24 And Z24i Engines

10 engines used, OMG huge and i can not guess them
lacking told or photo of one. ever.
I give up.

This website does not do well on abbreviations, - 'gcm - GCM'?

https://www.google.com/search?q=Turbo+diesel+5.9.+What+is+the+gcm

..

This could be a whole range of problems from lack of fire to engine to a bad fuel pump or pressure regulator in the TBI but if all of that is good then check the Cat. converter to make sure it is not plugged or the muffler. As I have 1994 Chev Silverado myself I know you can pull the 02 sensor out ahead of the cat. and it should run better not well but better. It will relieve the back pressure to the engine.

Are the injectors getting power and a ground signal from the computer ?

Try plug wires.

not compatible

should be under hood on or near fire wall, under plastic cover 

check if went from a V6 TO V8 need power two more cylinders

Sounds like the knock sensor has failed. It's on the passenger side at the bottom of the engine block, in front of the starter. One wire going to it. Have you checked the timing lately, maybe it has moved?

This injector set-up needs a specific fuel pressure supplied to the fuel rail to even start, much less run properly. The fuel pump is immersed in fuel inside the gas tank to keep it cool and not burn up. Running the fuel level low causes more heat in the pump and interuptions in proper fuel pressure. AC/Delco pumps have proven to be a reliable fix, the aftermarket pumps only last for a month or two sometimes. Check fuel pressure under the hood and power and ground to fuel pump at electrical harness at top of gas tank. This truck needs a fuel pump.