Method of compensating for injector aging

1. A method of controlling a fuel injector comprising:

monitoring engine speed;

monitoring engine torque output;

determining if the engine speed is within one of a plurality of predefined engine speed ranges;

determining if the engine torque output is within one of a plurality of predefined engine torque output ranges;

assigning one of a plurality of injector coking factors based on the determined predefined engine speed range and the determined predefined engine torque output range;

calculating a total injector coking factor based upon total operating time within each of the plurality of injector coking factors; and

increasing a duration of a fuel injection based upon the calculated total injector coking factor.

2. The method of claim 1 , wherein one of the plurality of injector coking factors indicates that no injector coking is occurring.

3. The method of claim 1 , further comprising comparing the total injector coking factor to a predefined maximum injector coking limit.

4. The method of claim 3 , wherein the total injector coking factor is set to the lower of the total injector coking factor and the predefined maximum injector coking limit.

5. The method of claim 4 , further comprising generating an increased injector duration amount based upon the total injector coking factor.

6. The method of claim 5 , further comprising comparing the increased injector duration amount to a stored maximum injector duration; and

setting the increased injector duration amount to the smaller of the increased injector duration amount and the maximum injector duration.

7. The method of claim 6 , wherein the maximum injector duration is based upon an emissions threshold.

8. The method of claim 6 , wherein the maximum injector duration is based upon combustion timing.

9. A method of controlling a fuel injector comprising:

monitoring at least one of engine torque output and engine speed;

determining if at least one of the monitored engine torque output and engine speed is within one of a first predefined range, a second predefined range, and a third predefined range;

monitoring an amount of time within one of the first predefined range, the second predefined range, and the third predefined range;

assigning a first injector coking factor if the amount of time within the first predefined range exceeds a first preset time limit;

assigning a second injector coking factor if the amount of time within the second predefined range exceeds a second preset time limit;

assigning a third injector coking factor if the amount of time within the third predefined range exceeds a third preset time limit;

calculating a total injector coking factor based upon total operating time within each of the first injector coking factor, the second injector coking factor, and the third injector coking factor; and

increasing a duration of a fuel injection based upon the calculated total injector coking factor.

10. The method of claim 9 , wherein the first injector coking factor indicates that no injector coking is occurring.

11. The method of claim 9 , further comprising comparing the total injector coking factor to a predefined maximum injector coking limit.

12. The method of claim 11 , wherein the total injector coking factor is set to the lower of the total injector coking factor and the predefined maximum injector coking limit.

13. The method of claim 9 , further comprising:

comparing a total engine operating time to a stored minimum engine operating time; and

setting the total injector coking factor to zero if the total engine operating time is less than the stored minimum engine operating time.

14. The method of claim 9 , further comprising generating an increased injector duration amount based upon the total injector coking factor.

15. The method of claim 14 , further comprising comparing the increased injector duration amount to a stored maximum injector duration; and

setting the increased injector duration amount to the smaller of the increased injector duration amount and the maximum injector duration.

16. The method of claim 9 , further comprising:

comparing the total injector coking factor to a previously calculated total injector coking factor; and

utilizing the previously calculated total injector coking factor if the difference between the total injector coking factor and the previously calculated coking injector coking factor does not exceed a stored threshold.

17. The method of claim 15 , wherein the maximum injector duration is based upon combustion timing.

18. A method of controlling a fuel injector comprising:

monitoring engine torque output;

monitoring engine speed;

assigning one of a plurality of coking factors based upon the monitored engine torque output and the monitored engine speed;

determining an engine operating time at each assigned one of the plurality of coking factors;

calculating a total injector coking factor;

comparing the calculated total injector coking factor to a predetermined maximum coking factor; and

increasing a duration of a fuel injection based upon one of the calculated total injector coking factor and the predetermined maximum coking factor.

19. The method of claim 18 , wherein the duration of the fuel injection is based upon the lesser of the calculated total injector coking factor and the predetermined maximum coking factor.

20. The method of claim 18 further comprising:

comparing a total engine operating time to a stored minimum engine operating time; and

setting the total injector coking factor to zero if the total engine operating time is less than the stored minimum engine operating time.