need injector help on 2000 c3500 5.7l pickup
 

I recently bought this truck it ran great, recently it developed a miss, replaced the plugs, wires, cap, rotor button, coil, ignition modual, fuel filter, and maf, still no better, so I put a computer on it and found it was #3 cyclinder was the problem, we shut the injector off and it didnt change a thing, the mechanic told me i had to replace the spider injection, I bought the new gm upgraded version that had actual injectors and put it in, still missing, I took #3 plug out and ran the truck with my hand over the plug hole for about 30-45 seconds, then shut the truck off, it had no scent of fuel on it. So I took the upper intake off, popped the injector back out of #3 and turned the truck over serveral times with no fuel coming out of the injector, what could this be?

I'm not sure if that test would really work. The FPR on these trucks uses vacuum from the intake (not a separate line like most) to regulate fuel pressure and with the intake removed there won't be any vacuum there. I would do a compression check on that cylinder first. If that shows to be OK then I would start tracing down wires to make sure none are pinched, corroded, or pulled from a plug. I would also check the big main plug that goes to the spider injector to make sure none of the tabs are bent over or corroded.