Boost gauge gets it's info from the map sensor... I've heard of people accidentally switching the plugs around between the map and barometer.. the plug will fit in each other.. do you have a scan tool? If the coolant temp is unplugged it will show -38 on the scan tool and the motor will run rich.. if you forgot to plug the map sensor in it will also run rich and your boost gauge will stop working.. and if you forgot to plug both in the motor will run extremely rich.. and that could account for the black smoke coming out of the exhaust and your boost gauge not working
