Have an 86 gt 2.8. Was running fine then just wouldnt start, tested it and found it had no spark, got icm tested and it was good so i replaced the coil. fixed the spark problem. now it tries to hit but sounds like it detonating. if i hold the throttle down it wil run very rough for a couple of seconds then die. It blows black smoke the whole time and by rough i mean backfiring violently the whole time. really sounds like the timing is way out. Was wondering how prone these things are to the chain slipping or loosing a tooth on the gear. Or any other ideas would be appreciated.
It's more likely that you moved something when you were playing with the ICM. Check connectors, make sure the pickup coil wire is not pinched under the distributor cap. Make sure the distributor did not rotate a little. Also, the ICM still might not be right....those tests are not perfect.