1993 Cadillac Sedan devillie blowing muffler

That may be difficult to address over this type of network. Some possibilities could include loss of cam timing due to worn chain/gears, wrong firing order, distributor that is installed improperly, possibly a faulty ECM or engine(ECM) ground, to name a few. Did this happen all of a sudden, has there been anything done to address it, or did it occur after some repairs?