Engine/Transmission (1998.5 - 2002) ruff idle

[UNKLRIC]

i have a 01 4x qc i bought it with 39k on it shortly after i got it it would intermittly idle rough on startup. i checked fuel psi and it had about 8psi and 0 at WOT so i changed the pu pump. it now has 16psi and about 10 WOT but it still intermittly idles ruff and is happing more often there is no codes and the scan data apears ok. . it runs great off idle. it just idles like it is missing

 

[Houser]

Might just be crappy winter grade diesel. Mine does the same thing in the winter. It get better if I put in an additive. Try Power Service, Cetane Boost and anti jell. Buy by the gallon and use 8ozs to the tank its cheeper that way.



Houser

Palmer Ak.

 

[Gary - K7GLD]

You may also be getting air in the fuel line from a leak between the tank and LP after the truck sits for a while...

 

[UNKLRIC]

thanks guys iv tried aditives in the fuel still the same it doesnt just happen when i start it it happens almost everytime i come to a stop and is driving me crazzzzy

 

[PRout]

Mine does the same thing.



Right after a stop, sometimes it will get a little rough on the idle, then after a few seconds it smoothens out. I notice it more now with the bigger injectors, but its not bad.



It feels like a gas motor when the timing chain gets loose, and cant hold a constant time anymore, and idles rough.



Installing the FASS seemed to help (a little).



30k miles ago, it idled totally steady, and the tach didnt move. Not any more.



Been a long time since theres been any additive run through the tank, maybe that will help some, but I suspect maybe its a sensor, the VP is starting to wear, or maybe a leaky injector tube.



Will try an oil analysis to check for fuel contamination.



It could be air in the lines, because thinking about it, mine does it after a startup as well. But FP is a solid 15 psi even under load.



Again, its not bad but same here, it bugs the heck out of ya.

 

[RW]

here are the the troubleshooting steps for a rough idle according To the cummins troubleshooting and repair manual.

1. engine is cold.

2. electronic fault codes active or high counts of inactive fault codes.

3. ecm is not calibrated or has incorect calibration.

4. engine idle speed is set too low.

5. air in fuel system.

6. fuel inlet restriction.

7. fuel lift pump is malfunctioning.

8. fuel filter is plugged.

9. fuel pump overflow valve is malfunctioning.

10. fuel drain line is restricted.

11. injector is malfunctioning.

12. fuel connector is leaking fuel.

13. fuel supply line restriction between the fuel pump and the injectors.

14. engine mounts are worn, damaged, or not correct.

15. moisture in the wiring harness connectors.

16. ess or circuit is malfunctioning.

17. fuel grade is not correct for the application or the fuel quality is poor.

18. overhead adjustments are not correct.

19. injector shim thickness is not correct.

20. static injection timing is not correct.

21. fuel injection pump is malfunctioning.

22. internal engine damage.



hope this helps.