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I got a new 2020 Z71 diesel a few weeks ago. Since I got it, it has averaged 21.7 mpg (display) with the best tank being 23.2 mpg (hand calc). Currently has 2000 miles. No CEL, it does not seem to shift the same as my dad's and brothers truck but other than that seems to be running fine. The truck is currently at the dealer since Monday, they are sending info to a GM engineer and so far say that they cannot find any issue.

My brother and dad both have Z71 diesels as well my brother has a 2020 about the same miles is averaging 26.5 mpg overall with more in-town driving. My dads is a 2017 Z71 averaging 26.7 mpg. Since my truck has been in the shop I have been driving the 2017. The same daily drive in the 2017 is averaging 27.9 for the week.

I have been searching the site for others having similar problems. I guess I need some sort of gauges to be able to see how often it is going into regen? any suggestions on which to get? any other suggestions or ideas about what it could be? I saw a thread about a leaky def injector, told the shop but not sure they even looked into it. After talking to them today it looks like I will have the truck back on Monday. Plan to drive it for a week or a tank or 2 and if there is no improvement try dropping it off at the GMC dealer next. Any suggestions or things to check before I take it back?
 

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I think you found the post I was going to mentor. Mr. Bones started it and it was on his truck basically being stuck in regen all the time. So it was burning more fuel constantly. Typically during regen you can smell it, mpg’s should drop 4-5 mpg vs normal. And you should also have more power and acceleration as the EGR valve closes.

If you can’t determine when you are in regen, press the shop to investigate it further.
 

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They say they have driven it a few times hooked to there computes and are not seeing anything out of the normal though if I remember right, Mr.Bones had the same problem with it acting fine at the shop. I think his was regening about every 150 miles or so. This could be what mine is doing, my milage seems to be low every morning and better throughout the day. I do not believe the shop has driven it more than 100 miles. Think I will need to get some gauges to get a better picture of what is going on with the truck.
 

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Instead of gauges, for $20 or so plus the $5 cost of the app, you could put a Bluetooth OBD2 transmitter on it and monitor the DPF soot level and regen (and of course lots of other stuff) your phone on your new truck and the even plug it into the other trucks and compare their regen interval to yours. You would know if it is in regen, and most importantly, how far it is going between regens. If I remember right, before it was tuned, my truck went 250 to 300 plus miles between regens, depending on driving.

These are the DPF soot level and regen formulas for the app:

8735
 

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Today I drove up to the job site And back in my dads 2017 and screen said I did 29.3. Picked the 2020 back up from the shop and have the fusion app with a OBDII reader. What pids should I monitor?
 

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Today I drove up to the job site And back in my dads 2017 and screen said I did 29.3. Picked the 2020 back up from the shop and have the fusion app with a OBDII reader. What pids should I monitor?
In OBD Fusion there is an SAE PID called "Average Distance Between DPF Regens". It's about 3/4 of the way down the list of SAE PID's. There's also an average time between regens just above it that may also give you some info.
 

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My 2017 Z71 4WD Crew Cab Long Bed has 38,000 on it. I generally get 22-23 around town if I'm not on the highway at all. If it's mostly highway 28-30 with the speed around 75, at 80 it goes down to around 27-28.
 

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Boost is under "Calculated PID's", Using the SAE ones you get absolute so you'll need to constantly subtract 14.7 to account for the weight of the atmosphere to know actual boost.

If just looking at them, launch OBD Fusion, select diagnostics, hit the menu at top right, select "Select PID's" then you will see them. SAE are the standard ones, I think these are as sent over the OBD channel. Calculated one are there too. There are a number of threads that have calculations you can do for "User-Defined PID's" as well. I find that the SAE EGT's are slow, too slow for towing so I use a User Defined one so I can have the refresh rate high. Also, soot level % is a user defined as well. Seems like the SAE ones have a refresh rate of like a second or 2.
 

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Just FYI, 33k miles on my babyd. I average 19.7 overall. 28mpg is my best empty mileage On the freeway. Around town it’s 21mpg. I tow a lot of he time. Pulling 4-6k lb. trailer I get 16-17. My computer says it’s getting 17-19, but calculations alway say different. Wish I could calibrate my fuel computer. Both a trip and mileage screen have different numbers and both over estimate what was actually achieved.
 
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