99 Civic Si w/B16A1. Check engine light on sometimes...Absolute horrible gas mileage...like 100-120 miles to the tank. Always smells like unburnt fuel, and when I get on it, black smoke comes out of the exhaust. I have replaced the map sensor. Can anyone help me out with this???

 

black smoke= burnt oil, maybe fuel if it was a ton.

 

The engine is running very rich. I guess you have converted to OBDI. Start by retrieve the CEL code(s) and clearing the ECU (see link in my signature). Again retrieve the CEL codes when the CEL goes ON again. Troubleshoot repeated codes.

 

Fuel pressure too high maybe. Check that the vacuum line on the fuel pressure regulator is hooked up.

Also remove the spark plugs and inspect them. If one is black and the rest clean, could be a bad fuel injector on that cylinder.