Slight miss at idle, poor MPG, sooty exhaust pipe, No codes. 250K

[Foggy]

Also think about cleaning your MAF.. Running oiled air filters is very common
for some of the oil to get onto the maf.. Clean it.
When was the last time you changed your upstream oxygen sensors????
They are pretty much a maint item anymore.. Good for 100-125K... They should
have been replaced at least once as reg maint since you have 250K. Get the good
ones: GM or ACdelco if possible. Just don't get the cheapo ones
Also would be a good idea to do a reset on fuel trims and ethanol % as mentioned.
The ethanol is calculated "virtually" on our rigs. So if oxygen sensors are crappy
you will get funky ethanol calculations

 

[j91z28d1]

yes, forgot about maf, I cleaned mine and could see it idling in a different part of the airmass vs rpm map and I don't believe it's ever had anything but a paper filter in it.


o2 are a good idea too, as they foul out over time, especially from how much oil these things suck thru the pvc system. they drift lean and the ecm throws fuel at it. also on these trucks that don't use physical ethanol sensors, fuel trims is what it uses to come up with E% content. so if sensors are reporting incorrectly, it can mess up the math and think it's running e when it's not.

 

[Tozan]

Thank you, I have never replaced those sensors I did clean and oil the air filter not to long ago. I cleaned the MAF when I did the filter I guess I will clean it again. I always say go back to the last thing you touched... That would be the air filter...