Fuel injecters

1999 chevy tahoe, 4wd, 350 5.7 112000 miles
truck was running bad, and really rich.
i was told that it waS MY INJECTERS.
i pulled the cover to expose the injecters.
the 4 injecters toward the back of truck
look like they are burned. Not the injecter itself
but the tube looking wire part.
does that mean those injecters are bad,
if saw what could have caused that
thank you