I have a 91 TBI 350 that started running really rough while driving down the road at about 35mph. It will not idle or run in the higher rpms, but can be kept running in the mid range. The computer gives no error codes. It is trying to back fire through the intake as well as exhaust. My first thought was a faulty ICM/distributor as it was one rusted piece of junk. A new distributor didn't change anything. The engine is still running rough timed from 0-4 degrees BTDC. Is there any way to tell if the timing chain has slipped without removing the cover?