I have a 1990 c1500 5.7 350 TBI, when I got it it had a crack in the tbi and sprayed fuel out the side. I just put a brand new TBI on and new injector wires/connector. Ran good this morning after I put it on both injectors sprayed. Then when I was leaving work I noticed the power loss got home and sure enough one injector wouldn’t spray. The driver side injector sprays, I swapped the connectors and it stayed the same driver side sprayed while passenger did not. Replaced all fuses. Still has this issue anyone have an idea what’s wrong?

note: new TBI came with new injectors in it

 

Hello! While I know nothing about a "1990 c1500 5.7 350 TBI"... I know a HECK of a lot about 1 of 2 TBI Injectors Spraying. This happened to and still happens with my 1992 Camaro RS with the 5L TBI. My issue was narowed down to likely an electrical wiring grimlin I believe after following ALL the troubleshooting you mentioned and having the EXACT same symptoms, I even swapped ECM's.

One thing not mentioned in your post was SES Light Codes? Example, Code 44 (runs lean when one injector dies).... Got any? Or you just notice a "loss of power"? How about your RPM guage when this issue occurs? Does it go crazy jumping around?

Here's what's in my GMSM for the 5L TBI

 

So, unless I'm reading this wrong from what you wrote, the harness is good, but the passenger side injector still does not spray. Either you have a bad injector on passenger side OR your ECM injector driver circuit may be bad.

 

I got no check engine light or code, just noticed the loss of power. My dash actually doesn’t have a rpm gauge

 

You can see if the injector clicks with a bit of a ringing sound when touched to a good 9 volt battery .If it does nothing it's bad

 

One injector doesn't spray. He swapped the injector wire harnesses, and the SAME injector still doesn't spray.

That eliminates EVERYTHING except the non-spraying injector. If it was the harness or the ECM/injector driver, the other injector wouldn't spray when he swapped the harnesses.

An ohmmeter could tell you if the injector solenoid winding was open. Compare resistance of the dead injector to the resistance of the working injector. If the winding tests good with the ohmmeter, the injector has to come out to verify that the screen isn't plugged. (A plugged screen would be exceedingly unlikely.) In that case, the injector "guts" are apparently seized.

I've seen injectors that were pulled off of vehicles, and stored for a long time. The remaining gasoline turned to varnish, and "stuck" the injector. I had one like that, engine ran like crap for five or ten minutes before that injector freed itself and began spraying. Has worked fine for many years since then.

But an injector that worked for awhile and then stuck...sounds like dead meat, to me. I think you're gonna need a different injector. Got a warranty on that "new" throttle body?