Friends 6.9 blows blue smoke, little black if you rev it. He is running wmo not sure what percent exactly at most 50/50 with diesel. He filters it with a paint strainer. I told him to switch to his front tank which is mostly diesel. Still doing the same thing. So he is going to try the diesel kleen trick overnight. It usually only idles for 10-15 seconds then stalls out. Changed fuel filter and does same thing. Im gonna help him tomorrow, what should we be looking for as the culprit? Truck has all original parts but mechanical fuel pump, just replaced several months ago. Truck has 92k miles. I got a 92 and 93 so I have spare injectors and injection pumps.

 

Could be air intrusion, but i dont think it would run that long. Try ATF/ diesel kleen and report back. When i was running WMO even over 50/50, it was dark grey not blue

 

Diesel kleen did not work. Ending up putting my one of my spare injector pumps on. Has much more power, but no its sucking in air somewhere. Going to start with replacing injector caps and return lines.