I have always been told not to replace just one injector, but on this 05 code is saying the #4 injector bad and as much as these things cost will it be ok to change out just one or go ahead and change all 6. Also should the injector wires be changed while in it???

replace all 6 injectors...i know it is expensive..but you will be glad that you did.

You can replace just one, but most people recommend all 6 becuase the others will probably fail soon after. You can pull them out and have them test and rebuilt, I know Don M and some others can do this. It would also be nice to know why they failed to see if you can do anything about it to prevent future failures.

I know the answer on the failure and was shown why they fail... I've been working on trying to find a exploded view of a CR injector so I could do a write up... The CR injector have a valve in them that is basically a BB in a seat. The electromagnet pulls the BB up from the seat causing there to be a loss of pressure above the pintle needle and POP the injector fires. The magnet releases the BB and seats against the hole once again and the injector stops firing. But now add <10 micron debris and it hones out the hole the BB sit on and the the BB can't seal the pressure causing the pressure to bleed constantly so the pintle is always bleeding fuel constantly. This what causes big issues with CR engine because once the injectors are leaking constantly it will start to wash out the piston rings and increase blow by... So like AH64ID he's added secondard filters and reduced the micron rating to 2-3 micron to protect his injectors...

as Mopar Man said add some extra filters. I have caterpillar 2 micron filters on my site that are better than airdog filters.Also I have nearly 100 new/reman/or tested injectors. I am not a fan of mixing SS with the original style injectors. If he has found the faulty injector he can replace just it. and hopefully go many more miles.