Can’t get mpg up

[EliteT660]

Hey everyone. So o have a 2009 t660 cm871 roughly 800k I started driving by the boost guage 58mph. Somedays I get 7.5-8 mpg and some days 5.5. Mpg. What am I doing wrong. I did egr tune. Replaced all sensors with Cummins oem. I keep boost close to zero while driving and never go over 20 psi while climbing. Any help would be greatly appreciated.

[Rawze]

Assuming it is not deleted... What does the regen history look like?. Maybe post a screen shot. ... or is it de-mandated?.

[EliteT660]

I don’t have insight set I’m working on that. But I have been getting random dpf/doc alarms and when I get under 5 mph I often get the hot exhaust light. So I’m assuming the system is regening to often

[Rawze]

(09-23-2023 )EliteT660 Wrote:  I don’t have insight set I’m working on that. But I have been getting random dpf/doc alarms and when I get under 5 mph I often get the hot exhaust light. So I’m assuming the system is regening to often

Very likely so, and how old are the DPF/DOC elements?. When was the last time you removed them and had them professionally baked out, de-ashed, and flow-tested?. They are due for this every 2 years or so .. BEFORE the check engine lights start coming on, or at first signs of it wanting a parked regen.