It looks like your computer may have a LED behind the round window, like the OBD0 fuel injection models for USA. On those, the LED blinks code numbers (if any are set) all the time the key is on, there is no need to close a jumper to read codes.

 

So if the error code led lights are not going on when I turn the car on and my car is blowing black smoke. Could it be that my computer could be the culprit??

What else could be causing the car to blow black smoke? I am only getting 300klms on a full tank when previously I was able to do 550klms.