ok this has Me a Bit Puzzled, i have a 1988 Firebird 305 TBI Auto. i was on a Small Road Trip 100 Miles Round Trip, done it multiple times in the car no issues and the whole way up the car was fine it ran normal, started comming back was doing about 55 on highway then out of nowhere Car went down to 1st redlined then temp shot from 190 to well past the end on the Gauge pulled over. had slight knock in motor and Coolant was GONE. filled it Before the Trip and topped it off before i left murray to go home so it was full only 15 Miniutes Before. im on side of Highway so i fill the Radiator Back up to Full and start it in hopes of atleast limping it to a Parking lot car had trouble Reaching 25MPH and after about 1/2 mile of flashers and coasting at 15 MPH on shoulder it died again this time ALL electrical went down, lights, windows, flashers, EVERYTHING. I know the Motor just Blew its Now Junk and i do have a Replacement However im confused about the Electrical could it be the CPU just died and cut the rest of the Car off? or is there a master fuse Somewhere i might have Blown.

 

Sounds like multiple failures , so lets start with the biggies first ;

The reason it dropped to first gear at 55 MPH could very well likely be that the plastic gear is gone bad on the transmission's governor . Yes there are other transmission failures that could cause this also but the governor drive gear is the most likely suspect .

Once the engine hit 5 or 6 K RPM it likely blew out some part of the cooling system with excessive pressure (that should have been vented by the radiator cap , but we all know how things don't always go as planned) and once the coolant was gone it overheated really quickly . Could be something external like a hose or even the waterpump seal , or it could be internal like a head gasket .

As to the electrical , just for a bit of an FYI as to how your system works , the computer (ECM) can not and does not control anything to do with the lights , windows , wipers , or anything else not directly related to running the engine . The fact that all electrical died means the battery , alternator , or wiring is suspect here . there is no one fuse , fusable link , or any function of the ECM whatsoever that would kill power to the entire car .

You have left out important details in your post , such as , after it dropped into first gear , HOW long did you continue to try to drive it with the RPMs sky high ? Was there steam from the radiator or anywhere around the engine (indicating escaping coolant) ? Did you attempt to refill the radiator once it cooled off to visually see if any dripping could be found ?

You say you have a replacement engine , great , that will take care of any engine damage , but neither the transmission nor the electrical will be fixed by installing a different engine . the electrical should be nothing more than routine troubleshooting for a trained mechanic and will likely end up being no big deal . The transmission on the other hand could be either very simple (governor gear) or very major (rebuild time) and you will need an experienced , HONEST , transmission shop's help if you not comfortable working on the transmission yourself .

Good Luck with whatever you find ...