Nissan Repair: engine take to much gass and give black smoke, rich fuel mixture, nissan march

Question
I have Nissan march model 1996 K11 it use to much fuel and exhaust gives black smoke.Some mechanic says this the problem of ECU and some says injector nozzle problem.What you say?

Answer
Hello -

First of all, pull each spark plug out one by one and examine the electrode. Are they all black, or just one or a few? If it is one or a few, then i would look for injector issues.

Does the engine idle rough? Does it miss up a hill or when accelerating? This will help the diagnosis.

Black smoke is carbon and indicates a rich fuel mixture.

Get back to be with your result, and we will go from there. Just to let you know, I will be on vacation this weekend.

Hope this helps
aloha
calvin