Chevrolet Repair: runs rich..., chevy s10 blazer, fuel pressure regulator

Question
QUESTION: Hi,
I have a 1993 chevy S10 Blazer 4.3L 4x4 auto. In the last month or so it started running rough on occasion. Then last week or two extremely rough all the time and just black exhaust. Code was O2 sensor rich. It only has one so I unplugged it and no difference. Does unplugging make a difference? I checked every sensor under the hood etc and checked the fuel pressure 55psi koeo, 50 koer, leaked down quite fast when doing koeo test. I then checked the fuel pressure regulator under the plenum and it was dry under there. I'm in the process of trying to remove the O2 sensor, but it is stuck. I cut part of the exhaust to check the cat and I almost thought it ran a little better, but once warmed up, it still was running shotty. Any ideas that you have, I would greatly appreciate.Thank you

ANSWER: Well you started in the right direction with checking fuel pressure. you said that it was 55 koeo, and dropped at a fast rate.  There's your issue.  If the regulator wasn't leaking chances are the regulator is okay, and you have a bad pump, or quite possibly and injector or two leaking at a fast rate.  These blazers where known for the bad injector assembly.  That's where I would start and that's why you would be showing a bad O2 sensor.
Jimmy

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QUESTION: Thanks Jim,
How can I be sure of which and if it is an injector? Is there a test of sorts I can do? Or pull them out and check the o-rings? Can you elaborate for me?
Appreciate it.

Answer
The only way to properly test for which injector it is, is to use a tech 1 scan tool at the dealer with a fuel injector break out box.  Some independent shops can do this just as well. Unfortunately you can't just pull them out and change just one on this year truck, you will have to replace the entire fuel assembly under the plenum.  There are no o-rings, they clip into the intake.  Sorry
Jimmy