My brother just put in a 350 into his 91 z28 (originally 305). He got it running using the stock electrical components and it ran for like a week, then it died like someone turned the key off. It wouldn't start back up so he left to call home and when he got back (~20min later) it fired right up and drove home fine. After turning it off at home, it wouldn't start any more and still won't. could it be a coil or something in the computer? thanks