Only runs with timing advance disconnected

I'm working on my brother's 94 s-10 blazer vin w. It broke down in Utah and he had the EGR and timing chain replaced. I went and got it after it wouldn't run. I replaced the exhaust system and the ECM, cap, rotor, plugs and wires. It runs with the timing advance wire disconnected, but as soon as you plug it in it stumbles, dies and won't stay running. It also is code free with the tan/black wire connected. Any ideas?