1988 Buick Century car puts out black smoke and dies

1988 Buick Century mileage: 133,000. My car has been to the Buick 3 times and they stated they don't know what is wrong. There are no codes. The car puts out black smoke and dies within 30-45 seconds but starts up right away and does the same thing. We replaced the mass airflow sensor, O-2 sensor fuel pressure regulator air filter. The injectors are about 6 months old. Neither the dealer nor I know the problem. The dealer now wants to replace the computer as a GUESS and last resort.