I had a problem with my 99 bonneville 3.8. it was the . I unplugged it and it worked!

If one injector is out of pattern with the rest, I would be highly suspicious of it, especially if you double and triple checked it.

That would imply also that the car should start and run with injector 5 unplugged.

If one injector is reading 3.5 ohms, that is a problem.......

There is a quad driver in the ECM.....and it controls current to injectors 1-3-5....normally, it would detect approximately 3 amps on that circuit, because 12 volts across each injector, at 12 ohms, would produce 1 amp per injector.....in parallel they produce 3 amps total......but if one injector is say 3 ohms, and the other two are 12 ohms, this produces 1+1+4=6 amps, and the quad driver will see excessive current and shut down the circuit, thus killing all three injectors....

You should replace that injector......you have to pull the whole fuel rail......with the engine being that old, those o-rings on the injectors all have to be replaced.....there are two per injector.....on the end that goes into the rail and on the other end that goes into the lower intake......sometimes when you pull the rail, the o-rings are hard and dry, and it seems like the injectors do not want to come out.......since you have the upper plenum off, tape the hole openings of the lower intake so dirt can't get in.....then use a blow gun to remove debris surrounding the area where the injector enters the lower intake(so any debris will not fall into those holes).....then I use PB Blaster, and spray where the injector enters the lower intake.......this helps to loosen up those old o-rings.....remove the two bolts holding the rail in place( you also have to disconnect the fuel lines, and replace any o-rings)then with a small pry bar, get it positioned between the lower intake and the injector and gently pry up the injector.......work your way all around, and they will eventually come free.......sometimes the lower o-ring stays in the lower intake...carefully remove it, don't let it fall in.....

Wipe clean the injector holes in the lower intake carb cleaner in a rag......I put petroleum jelly on the upper and lower injector o-rings, to aid in installation back into the lower intake and the rail.......

If you don't replace all the old o-rings, you stand a good chance of a fuel/air leak.....