Running Rich

[John Uribe]

Its time for emission testing again and my 88 5ktq failed.
It seems to running way to rich (the inside of the tail pipe
is covered with black soot). I am considering replacing the
injectors since the car has 160k on it, but I want to try
and make sure that it will help the rich condition. I know
that leaking injectors will make the car hard to start, and
for the most part my car starts well (now and then, it
cranks for 4 or 5 seconds befor it starts).

So the question is: What is most likely to cause a rich
condition?

John