SAAB 900 running rich

My 1991 SAAB 900 seems to be running extremely rich. I have about 230k miles on the car. No fault codes have been set. Black smoke from the exhaust pipe. Will not run abaove 3k rpm. I have just ordered a fuel pressure regulator but inspection of the one I removed does not indicate that it has failed. Any ideas?

Some possibilities could be seriously retarded ignition timing, plugged fuel return line to the fuel tank, or a clogged catalytic converter although I’m kind of leaning towards the latter.

This could be checked with a vacuum gauge and if you do a lot of your own service work buying a vac. gauge is highly recommended. It’s one of the most valuable and helpful tools you can own; and they’re cheap too.