I can't give you a whole ton of info on this, here's what I know, hopefully SteveB or Benzmac can help more:
On your 85, probably about all the OVP is being used to power up is the engine control module. If the fuse is blown (or missing) the engine runs without the engine control module in sort of a "limp home" mode called Fixed Operating Mode, or "FOM". There is no Lambda control, it uses the same mixture setting regardless of operating conditions, like engine coolant temp or ambient air temp or the like, I don't even think it uses the airflow meter in FOM. So you're not really getting an ideal mixture like this, so poor performance, fuel mileage, poor starting (especially when cold). I am unsure why it fails to start or run when the control module is powered up. My initial reaction would be possibly the air flow plate (base mixture setting) is way way off, either rich or lean, but in FOM it will at least run, if not the greatest.