Originally Posted by Front Range 4x4
Quick update - Air Care Tech found:
1. A bad EGR solenoid. I guess when I found the bad EGR valve I stopped trouble-shooting.
Didn't really matter, hardly changed the NOx reading when I replaced it.
2. It appear to be running lean - not sure how to resolve that yet.
3. Recommended going back to dual cats,
Scotty is warrantying my year old cat tomorrow. I really think that may be the problem but I claim total ignorance and frustration at this point.
If that doesn't fix it I have an appt at Colorado Car Clinic next week. I stopped in there and Dave (IIRC) was good. Not very surprised to see another "Land Crusher" outside his shop.
If you are running lean, and you already replaced O2 sensors, I would look at the injectors.
Upstream of injectors would be fuel flow (think pump and filter) and pressure (think fuel pressure regulator).
Have you checked fuel pressure?
How many miles are on your injector?
I think you can richen things up by tweaking the AFM.
Keep us posted!