Fluctuating Gas Mileage

[Mfgilbert79]

Hi all,

I’m new here so be gentle until I get my feet wet.
I’m driving a 2020 2500 6.7L Cummins.
I have been having wierd mph fluctuations on the computer. I go from 21-23mpg to 10-12mpg every couple of days in the middle of a drive. And once it falls down, it does not recover.
I have replaced the fuel filters and all other maintenance is up to date.
I was scrolling through the truck data while driving through this problem today and noticed while idling truck seems (I’m not sure about this just seemed high 1500ish I think)to be running a little high rpm wise. Also while coasting my boost gauge was showing 3-4lbs of boost.

Any ideas? Any post floating around about this here on the forums?

 

[KKBB]

My guess would be when you see the drop in MPG, or the high idle RPM the cummins is doing a regen.

 

[yakalong]

Have you hand calculated your mpg or is this just per what the computer shows?

 

[Mfgilbert79]

Only what the computer shows. No I have no hand calculated the mpgs.

 

[Mfgilbert79]

My guess would be when you see the drop in MPG, or the high idle RPM the cummins is doing a regen.

 

[Mfgilbert79]

Thank you. I did a little reading about that and it makes sense.