2021 Tahoe LT Duramax mpg/mpd increase after maintenance and software upgrade

[Alexnorton]

Last month I had my Tahoe 2021 LT Duramax for routine maintenance oil change in the dealer.
It's mpg/mpd changed from avg 30 to 26.
The dealer said they didn't do anything.
I'm not sure what I should do.
Does anybody have a similar issue?
Is it maybe because of bad injectors?

 

[DuraYuk]

Last month I had my Tahoe 2021 LT Duramax for routine maintenance oil change in the dealer.
It's mpg/mpd changed from avg 30 to 26.
The dealer said they didn't do anything.
I'm not sure what I should do.
Does anybody have a similar issue?
Is it maybe because of bad injectors?

No. There are 1000s of things that could have led to your decreased mpg. If you don't have any warning lights doubt it actually has a mechanical problem.

Just drive it and see. Check your tire pressure.

 

[B-train]

Also, has your fuel filling changed locations/vendors?

If they did a new engine calibration, then YES it could affect MPG. If they did that, it's most likely an emissions "upgrade" that as we all know is a complete joke. Think VW.....all the cars with "corrected" calibrations got worse MPG.

In the future, if it's running well, tell them no more refreshes without approval and letting you know what it's supposed to correct.

 

[StephenPT]

Going from straight diesel to B20 will give you that kind of drop in fuel economy. Do you keep track of where you fill up and did you fill up shortly after visiting the dealer?

 

[Alexnorton]

Thanks guys
Fortunately, I don’t have any warning lights on.
Tire pressure is ok
Didn’t change fuel type.
I drive it about 1000 miles which I did it more than 10 times in the past and filled the tank from the same gas stations. But the results are not favorable.
With a full tank I could drive around 767 miles and now it’s around 550 miles.
I’m not sure if they did any engine calibration, but definitely I feel it has more power and I can’t hear it’s turbo noise.
If anyone has any recommendation regarding the engine calibration or anything that can help I appreciate it to share.

 

[Stbentoak]

Well 550 to 600 is much more realistic. You can get 30, but to AVERAGE 30 is a high anomaly.
I avg 24-26 and I'm very happy with that...

 

[Brand0n]

767 miles?! Agreed 550-600 has been my experience…

 

[Alexnorton]

 

[DuraYuk]

Thanks guys
Fortunately, I don’t have any warning lights on.
Tire pressure is ok
Didn’t change fuel type.
I drive it about 1000 miles which I did it more than 10 times in the past and filled the tank from the same gas stations. But the results are not favorable.
With a full tank I could drive around 767 miles and now it’s around 550 miles.
I’m not sure if they did any engine calibration, but definitely I feel it has more power and I can’t hear it’s turbo noise.
If anyone has any recommendation regarding the engine calibration or anything that can help I appreciate it to share.

Your 24 gallon gas tank is averaging 777 miles? That's over 30mpg! That's crazy! I get 30mpg average on highway around 80mph.

 

[martinajm]

I barely get 700 miles on my 28 gallon tank in my XL. Seems to me like they fixed an overly optimistic fuel economy calculation. Do you have hand calcs for fuel economy before and after the change?