What's causing my engine to run rich on 1992 Chevrolet Blazer

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The check engine light is on - code 45 I replace the o2 and the catalytic converter. I've read that the fuel injector or fuel pressure regulator may need replacing, but the book says it should be done by a technician.. Can this be done by me?
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I am assuming that your 1992 Chevrolet Blazer is a small Blazer with a V6 engine, not the full size version. If I am wrong please let me know. The fuel injector and pressure regulator are located under the upper intake plenum. The particular fuel injector includes the fuel pressure regulator. Replacing the injector is not a difficult job for an experienced technician. You will need to decide for yourself if you want to take on the job.
Oakman, The engine is 4.3L V6. It has a CPI. Will this make a difference in my being able to replace the fuel injector or fuel pressure regulator? I guess that is why the repair book said to take it to a professional. The vehicle is old, but we need to keep it running. I'd rather not put any investment in professional repairs especially with the age of the vehicle.