[sierrap615]

91 and 92 S-series used different crankshafts and are not compatible with other years, the toner ring for the crankshaft position sensor is 10 degrees of and the 91/92 PCMs are programed to match. therefore use a 93+ crankshaft with a 91/92 PCM or viseversa and your base spark timing will be off 10 degrees(advanced or retarded depending on which combonation, can't remember which is which) throw in the reading from the knock sensor and who knows how far your timing is off.

so what year was the donor engine? if the crank does not match the PCM there is no easy fix, ether the crankshaft or PCM/wiring harness needs swaped.