My 1990 riviera will run great, as you are going down the road it will shut off,but crank right backup. whats wrong?

Buick 1990 Riv; stalls unpredictably; cold, hot, warm, running or not running may not start; engine turns over; no spark; good crank and cam sensors, and signals; when stalls and no start condition, high speed pusher fan starts, near ICM; and 11 volt signal on the fuel injection control wire from ICM to ECM with ignition on and no start condition when it should be .08 volts and 6 volts running. Only fault code on cars' OBD, b334c loss communication ecm to bcm. Then fan will go off and it will run for a while. Cleaned ecm and bcm connectors and grounds. new ICM What is this problem?

Check the ECM part number. If it is a 1228253 that is your problem. get a 16198264 the other number does just what your car is doing. I worked at a Buick dealer and know about the problematic 1228253 ecm.