emc issues? or bad wiring

my husband and I just rebuilt a 4.3 tbi for my 88 blazer intalled it at 8 degrees advanced like the specs showed, runs great but when you connect the ecm the timing will advance to 16 degrees advanced and causes spark knock engine to over heat and will show codes for temp sensor, vss, low voltage from the map sensor we've tried clearing the computer many times and it still wants to do this. what exactly could it be?

Are you disconnecting the ECM timing wire while you are timing the vehicle?

You set the timing to 0 degrees TDC and then plug in the wire.

The wire is for the timing advance.