Volvo: Engine running rich, air flow sensor, oxygen sensors

Question
I own a 1977 S70 non turbo. It's fuel consumption has become excessive. Black smoke comes from the exhaust. The car still has plenty of power. I was able to get 500kms from a full tank but can only get 380kms now. The oxygen sensors and air flow sensor have been replaced to no avail. The oxygen sensors get badly carboned up. The exhaust front silencer has also been replaced.

Answer
Howard,
I am not sure of your vehicle. Here in the States we have S70's starting in 1997, so I hope that is what you have. Now there should be codes that can be read in the control unit and that may leed to a failing part. Read those codes and follow them. Check the fuel pressure is it excessive? It should only be 42psi or 2.8 bar. Is the pressure regulator leaking fuel through the vacuum line? Any bare wires shorting out keeping the injectors open? These specs are for cars that have the Motronic 4.4 system. That is the system here in the States.