Lost MPG Solved!

[JBonpua]

About 5 months ago I noticed a big drop on my MPG calculation (hand calc) after going to the dealer for an unrelated issue. The dealer SOP flash the ECM. I’ve lost about 2. 5 to 3 MPG on my first and subsequent fill ups after the trip to the dealer. This is a significant drop in fuel mileage.



I normally drive right at 60MPH on the highway and always drive on the slow lane. . Duramax and Powerstroke drivers always pass me up and give me that “I’m faster than you” look. I’ve noticed that after the trip to the dealer, I’ve been keeping up with traffic for the most part. I suspected right away that my speedometer is wrong. Sure enough after I plugged in the Smarty to check the tire size, the tire size went back to the OEM setting from my 37”. Changed the size to my current tire size and verified my speedometer with two GPS receiver.



Not only was I traveling faster, my odometer was telling me that I traveled shorter distance than I actually did. This is a double whammy. So be aware that if you are running taller tires and you set your speedometer to that tire size and your ECM get flashed, your tie size might have gone back to OEM size.

 

[MChrist]

Thanks for the heads up! It's always good to check the simple stuff. Like getting new tires, most people say your mpg goes down because you have softer rubber, since it is deeper tread, which may be true. However, you never hear anybody mention that since your tire is also turning less, due to the larger circumference, your odometer indicates less miles traveled over the same distance. Therefore, your mpg will suffer.

 

[InfernoB]

Was this the flash so the Republic can perform a proper smog check?



Did you notice anything else after the falsh?



Thanks.

 

[Newt]

So be aware that if you are running taller tires and you set your speedometer to that tire size and your ECM get flashed, your tie size might have gone back to OEM size.

DUH, this came as a surprise to you? :-laf



Newt

 

[JBonpua]

DUH, this came as a surprise to you? :-laf



Newt

Yes it surprised me. I did not think flashes would affect the tire size setting. Did you know? Are you running taller tires where you set your speedometer to the taller tires and got flashed. After the flash you verified the tire size loaded in your ECM with your Smarty? Are you just being a smart guy? I hope not.



The point I tried to come across to fellow members is the issue with tire size resetting to OEM size after a flash and not when running taller tires your speedometer will be off. I am not very smart but I even know that.

 

[Prairie Dog]

There's been many, many threads regarding flash updates and never has a tire size change been mentioned. So yes, this is news to me too.

 

[Newt]

Anytime the dealer does a flash on the truck, everything goes back to OEM specs. If your still under warranty, you should put the truck back to stock before taking it to a dealer for anything. Unless they're a complete idiot, they knew you had used a tuner on the truck.

Newt

 

[JBonpua]

No not all flashes affect the tire size as my ECM been flashed before and never affected the tire size. SOP Smarty goes to stock whenever I take it to the dealer.

 

[HHhuntitall]

... . don't forget the "Dealer" is not seeing anything the TECHNICIAN doesn't want him to see..... if the flash doesn't contain an ABS reset code, even on new trucks, it doesn't change. If the Tech saw a trouble code, wanted to clear it and try to duplicate it in a test drive, which is very common after programming with an aftermarket box, and then resetting to stock, the Tech may or may not have entered the ABS line code sets. If he did enter them, and there is a non-stock parameter setting programmed, it may or may not be reset by the tech. If the tech just does a complete restore and update, especially if he suspects an aftermarket programmer has been added, he clears everthing, including the evidence an aftermarket programmer has been added..... while this is annoying to some, the tech may have thought he was actually helping you... ... . many of them do actually TRY... .

 

[SRadke]

You didn't notice it was turning 200 rpm faster than usual? I drive by the tach, the speedometer is just a luxury.

 

[JBonpua]

Honestly no I did not even looked at the tachometer as I pay attention to the speedometer.

 

[AH64ID]

IIRC the 06+ trucks can only be set to OEM sizes by the StarScan, which is 245 or 265 on diesel trucks, and can be manually set to 285's (Power Wagon), but isn't part of the OEM flash.

 

[CDonaldson]

I had the dealer set my tire size manually to the 285's when I put on my 315's, that was the highest setting they could do. When they did a 'total' ECM upgrade reflash a couple years later my tire size remained at the 285 size. When I got my Smarty Jr, I set the tires to the correct tire size. So, I think that a flash must change the Smarty settings and NOT the dealer flash?? I really do not know this for sure, but that's what happened to me/my 2006.



Also, I had them turn ON the high idle feature, it remained when they did the flash too.



CD

 

[surfbeetle]

I had the dealer set my tire size manually to the 285's when I put on my 315's, that was the highest setting they could do. When they did a 'total' ECM upgrade reflash a couple years later my tire size remained at the 285 size. When I got my Smarty Jr, I set the tires to the correct tire size. So, I think that a flash must change the Smarty settings and NOT the dealer flash?? I really do not know this for sure, but that's what happened to me/my 2006.



Also, I had them turn ON the high idle feature, it remained when they did the flash too.



CD

I work in IT and I can tell you from a computer standpoint is that anytime you are doing a flash or an update of some sort, recommended procedure is to always backup your stuff. In terms of a firmware update, some vendors will simply state that you should write down the settings as there may be no way to run an automated backup. So what we don't know is if the technician was thorough enough to check your settings prior to the flash of the CPU and then manually re-enter them after the system came back up. If the tech doesn't care, they may be just doing it as fast as possible to get onto the next dollar.

 

[JBonpua]

Makes sense and that's probably what happened