My car is a Nissan Altima 2006 model. I had changed its mufflers before 2 months. When I felt the vehicle emits excessive smoke, I had an emission test from Etobicoke. The smoke emission rate was high. What can be the reason behind this? Is this because of the mufflers or some other things? Normally it happens due to piston failure. But I have done all those works before 3 months. If somebody know about this, please help me to resolve this. If it is due to some minor problems, I think I can fix it myself.