I recently swapped engines in my Trans Am from a 1988 305 TBI to a 1986 305 TPI. I had the wiring harness converted to TPI and retained the stock pigtails for the 1988 distributor (remote coil). The 1986 engine had a coil in cap distributor. The computer is a 1986 TPI computer. Now I don't have any spark advance except when I unplug the plug on the passenger firewall used for setting timing, but spark only advances until about 3500 rpm. What should I do?