Was it running good when you got it from previous owner? Did you get codes with a scanner? could be shorting out wiring, wiring plugs loose, bad grounds, computor bad, re-set timing to 10btdc, put in some injector cleaner or some SeaFoam in tank and run some thru engine intake. how's the O2 sensor, map sensor, IAT
sensor on intake manifold. alternator putting out good? try one thing then something else til you find it. this what I had to do to my '88Bronco II 2.9 when I ist got it. blowing black smoke(running rich),changed all sensors, O2 sensor,map, TBI sensor, IAT
, new battery cables, battery, plugs etc. last resort was the computor inside right kickpanel,,it was damp and had shorted out due to moisture that gets in there after 24 odd years. try that too.