I have yet to replace my fuel injectors at 436000 miles however I think they are going bad. What are some of the main symptoms of bad injectors and also when they start to go bad do they quickly go bad or does it progressively get worse?

 

They can die fast or slowly.
Main symptom is excessive smoke especally on start up.

 

Will the smoke be white or black?

 

Bad mileage will come first without noticing much smoke, but eventually they will smoke more and more.