I had the tranny replaced in the truck several months ago. Since then, it idles lower in gear, which is understandable with a tight converter. The other day, I noticed that it seems to have a miss at idle. Not real noticeable. It carries thoughout the RPM range, just not as noticeable. Bad injector? The injectors are stock with 265000m and never been serviced? What could be the other possible problems?

 

A wide open question and you are probably right that it is an injector, but a valve starting to burn would also act that way. Run the valve adjustments also.

 

thanks for the info... Plan on looking at it this weekend. How can I differentiate between a burned valve and a bad injector? Any other symptoms I should look for? I know I haven't provided enough info for a diagnosis, just looking for a point in the right direction.

 

Ok to start with to check for which cylinder let it idle with the miss. Crack each injector line loose and when you open one it will change the running as it loses that cylinder. When you hit the right one it will change little or not at all.

You can pull the injectors or the one from the bad cylinder and Cummins will pop test it. Or an injector shop can do it. The valve can be determined by a compression test. I would start with the injector. I am not big on 12 valve systems but from what I have been told there can be a bad valve at the output of the injector pump also that could make it miss.

I would start with the injector.