Well, maybe they changed the way it calculates. Mine will only do that when you push reset, and then shortly thereafter. Once it has some time on it and has calculated thousands of times, the average doesn't change much. Mine is consistently 11.9 to 12.5 in my normal driving, which is dead on with my calculations when I do them. Mine is very accurate.

2006 Mega Cab

 

My 04 Hemi Ram in the week I've owned it has been saying an average of about 12.5mpg (10.2mpg when my gf drives it) and suddenly today after switching to Shell Gas from Kwik Trip Gas (A Wisconsin Gas Station Chain who brags about having the best gasoline...my @$$!) I've been getting 17mpg in the city going 40-45mph with mostly green lights lol. Pretty proud of that, not sure if its the gas, new pcv valve or the fact I've been trying to save the back tires from burning off after the last fill up.

 

Yeah, I guess going back and re-reading it a couple of times...it makes sense that you were talking about the speed at which you get the best mileage out of. I apologize. I'm also happy to realize your not as gullible as I was hoping you werent..haha

Right around 62-63mph my truck gets the best mpg's as well.

 

Alright, I installed the new unit and road tested it. It said... (drum roll please) 3 MPG's. Yes, that's what it said. Now, my V10 is a gas hog, but I know that's way, way low. The one that was in the truck read 11-12 average, which agrees with the fuel tank. I flipped to average MPG's and it agreed with the Instant reading. So I got home and disconnected the battery for 30 minutes, and tried again. Still, the same thing. I thought these things were slaved off of the PCM?!? I thought maybe recalibrating the compass may cause the info center to re-learn, but I am kinda upset....

 

Lol, that would be funny! I just had the idea of someone with a V8 and super sized tires bragging about 62 MPG's!! I think I would literally soil myself laughing!!! I work at Advance Auto Parts and I would like to think I've heard it all, but that would literally take the cake!!! LOL! LOL!

 

Alright, I've tried to be patient and have gone through several tanks of fuel, and it still says 3 MPG's. I've disconnected the battery for an extended amount of time. What can I do to fix this? Can the dealership re-flash it? Or is there something else? These things CAN'T be vehicle- motor- transmision specific..... Can they?!?

 

Well, they must be wheel size specific! How else would the computer know how many revolutions it takes to go 1mile? Tire size. If you have larger tires, the computer would actually read a lower mpg readout because it thinks your taking longer to get there, when in fact you got there sooner because the diameter is larger than stock.
Your tires look a bit bigger than stock. So, that could be one contribution. Bad or old 02 sensors can hinder mpgs too.

Are you sure your calculating it right? At 3mpg on a 34gal tank, you'd be completely empty running on fumes after 102miles. I find this very hard to believe! That means its costing you $4 to drive 1mile?? Better get your bicycle out..lmao
How many miles are you getting per fill? When you fill back up, how many gallons did you put back in?
Example: On average, I fill up my car 12-14gallons. it has an 18gal tank. I would need to read current odometer and divide it by how many gallons I just pumped in. i.e.12-14

 

Maybe someone else can shed some more light on this, as I am not for sure, but I have an extensive background in electrical/electronics, just not very specific to these trucks...but They could be "computer"specific, as I understand most of these trucks of OTIS overhead displays, but the high luxury like laramie have EVIC...and you may not be able to swap between them as the computer in the truck may not be "speaking the same language" that the display understands. BTW, which AAP do you work at? I work at 6779 in Michigan.

 

I get roughly 380 to 400 miles on a 34 gallon tank of fuel. That is nowhere near 3 mpg's. And the truck in my signature is another one. My 2003 has stock tires, and the speedometer's dead on....

 

Grrr. I want to put the old one back in now. And I work at 4840 in Leland, NC. But I just told my manager I wanted to go from full time to seasonal. I was getting driver's pay while working as a CPP. What's your position?