1991 Mazda B2200 Fuel System

My father has a 1991 madza B2200. He had been driving home, 20 miles highway driving. As he slowed to turn home the truck started missing and died. He had trouble restarting it and black smoke poured out of the exhaust. We replaced the O2 sensor and spark plug wires and clean the plugs. This did not help. Engine will run fime for about 30 seconds then it turns to run very rough and black smoke pours out of the exhaust. No trouble lights have come on to indicate a problem we could use a code detector on. A guess has been to replace the fuel pressure valve(?) But it is kind of expensive and would rather have some bases to try this or something else as opposed to just spending money.