Overhead MPG Accuracy Fix ?

[BTesluck]

Is there any way to calibrate or adjust the accuracy in the overhead readout of my mpg on my 2004 CTD? This is the only thing that bugs me about this truck. I know, its a truck, but darnit if I put a gadget in my truck, I want it to work correctly. So why don't Dodge do the same. When it was new, it was within a mile to gallon. It has 93000 on it now and its a tad bit more than three miles per gallon off from calculations. I talked to my dealer and he said its just an average so don't worry about it. WELL , I drive it on the same route everyday and it is getting worse. Its agrivating. I pay this much for a darn nice truck and my overhead says i'm getting 21mpg when it always calculates at 17 to 18. Just bugs me and wish I could fix it. Anybody have the same problem or a solution?

 

[JJPage]

The more I reset mine, the closer to what is accurate it gets. It has always been more complimentary to the truck than hand calculating.

 

[Regcabguy]

With the latest Smarty update my overhead actually reads lower than hand calculated. Go figure!

 

[CVonRitter]

mine is just now started to read 6 to 12 mpg but i am geting over 17+mpg what do i do (i have hit the reset . . no diff. )

 

[CVonRitter]

with smarty chip and also put it back to stock ... . same readings...

 

[AMink]

I wish the 06 had a "what it is right now" mileage option. You start the new tank where the old one left off. I would think that computer would know exactly how much fuel is getting squirted in, no matter what's in the tank. It should be super accurate. Guess it's just a gadget with no real meaning.

 

[Kry226]

I think many times it comes to tires and how worn they are.



For example, when I put my BFG 315s on, I had the pinion factor changed to 601 revs per mile. The overhead was dead on, within a couple of tenths. Now that I have 50k on these tires (almost worn out), I have noticed that my overhead is less accurate than it was. I am sure the 601 pinion factor is no longer true due to most of the tread being worn away.



I have a good feeling that when I put new tires on, whether I stay with the 315s or go with a new size and reprogram, my overhead will get closer to and almost equal my hand calcs again. FWIW.

 

[rweis]

If you reset the tire size until you get the actual mpg in the overhead will it screw up the odometer? and speedometer? or are they seperate "displays".



Bob Weis

 

[BTesluck]

I don't have a Smarty or any chip other than factory. Sounds like I can't set anything. Am I right?

 

[DrDiesel]

I don't have a Smarty or any chip other than factory. Sounds like I can't set anything. Am I right?

The overhead display is very accurate. The MPG from the overhead reading is the current average. NOT MPG`s per tank.

 

[RHestand]

The overhead display is very accurate. The MPG from the overhead reading is the current average. NOT MPG`s per tank.

Current average being from reset to the next reset?

 

[rweis]

DrDiesel -



What I have observed in my own case:



Most times the overhead error is directly attributable to "bombing". When you put in "bombs" you wonder what hp gains you really have. I think you can take the overhead error and directly attribute the error to modifications you have done.



In my case I added DD2's (80 hp), HTB2 turbo, 4" exhaust, ... see sig. My error is close to 25%. I mentally reduce average mpg by 25% and am very close to the hand calculated mpg over 85 K miles.



I think that the ACTUAL fuel flow is not measured, but predetermined to be the stock value in a stored table. The miles driven probably comes off the ring gear sensor. The distance remaining is probably based off the "calculated" mpg times a fuel remaining predetermined table based on the OEM fuel gauge position.



So, working backwards, since I think there are predetermined tables for the stock truck, you can hand calculate your ACTUAL mpg, compare the stock mpg to your hand calculated mpg and you get the value of the "bombs" in % greater than stock.



my . 02

Bob Weis

 

[NNovak]

rwies,



Great theory but then why is my stock truck off by so much.



I have hand calculated every fill up over the last 4,000 miles, reset the MPG on the overhead every time and I am 3-4 MPG off every time. 3 when it is a in town tank and 4 when it is at least half Highway. I was 3. 5 mpg off when I did town and used 4x4. Every time the overhead is reading High. No mods unless you count he K&N air filter as a mod.



The part that confuses me so much is that there are trucks like mine with overheads this far off and other truck that the owners say are only 1mpg off. One would think they would all have the same % of error.

 

[DrDiesel]

CURRENT AVERAGE

The current average determines what the EST. MTE is. Hence the word EST.

The overhead will never be close to a hand calculated per tank. It`s not designed to display MPG per tank. It only displays the current average.

It takes the current average and multiply`s that by the remaining fuel load as input from the fuel meter/sensor and derives the MTE data.

It`s all related to the current average. The current average has nothing to do with per tank MPG. . :{

 

[NNovak]

IF that was the fact of current average then it should change regularly, so when I put my foot in it is would go from 17mpg to 10 mpg as currently foot in throttle you are getting crappy milage and when I have my lightly on the peddle cruzing at 50mph, it would say 24mpg. But it doesn't it changes as you put miles one and the more miles the slower it changes, Thus the average since last reset.

So if it is current average form last reset then when I reset the MPG at a full tank, drive 200 miles, fill up with 10 gals, my hand calc would say 20mpg and the Overheads current ave since last reset of 200 miles ago should say 20mpg.



basically, some computer guro out there needs to figure out how the ecm is getting the info and computing it then do a new algerythm to program the ecm with so make it correct. I don't think Dodge is going to do it.

 

[Vaughn MacKenzie]

To me CURRENT AVERAGE means that, what am I getting right now, not what have I been getting since I last hit the Reset button. In other words what is my average MPG for the last 10-30 seconds. . . the Dodge overhead computers used to give you this.

The time base to calculate average that Dodge uses is the amount of time between hitting Reset. Pretty lame IMO unless you are only interested in MPG for a certain trip, between fillups, etc. The longer you drive the less impact sudden changes in driving will be reflected.

IMO if you only reset the overhead at each fillup then might as well call it TANK AVERAGE or MPG per FILLUP

 

[DZLROKET]

My experiance: (06)



The overhead gives you average MPG since the last reset.



The shorter a time since the last reset the more the current MPG affects the readout. IE: going down hill =65 MPG. uphill=13 MPG.



The longer a time since the last reset the less fluctuations you see on the readout since there is more "history" to take in to account.



Therefore: if you reset at fillup and do not reset untill next fill up you have (just before reset) the average MPG of the last tank full.



JMNSHO !

 

[RKershner]

mine shows 2 mpg than the hand calculations and the speedo is 2 mph faster than my gps

 

[DrDiesel]

IF that was the fact of current average then it should change regularly, so when I put my foot in it is would go from 17mpg to 10 mpg as currently foot in throttle you are getting crappy milage and when I have my lightly on the peddle cruzing at 50mph, it would say 24mpg. But it doesn't it changes as you put miles one and the more miles the slower it changes, Thus the average since last reset.

So if it is current average form last reset then when I reset the MPG at a full tank, drive 200 miles, fill up with 10 gals, my hand calc would say 20mpg and the Overheads current ave since last reset of 200 miles ago should say 20mpg.



basically, some computer guro out there needs to figure out how the ecm is getting the info and computing it then do a new algerythm to program the ecm with so make it correct. I don't think Dodge is going to do it.

Sorry, but that`s not how it works. Hit the rest button and try your theory and watch it change. Current average is not instant average. The longer between reset the longer it takes to show an average change.

I have a 2007 Honda Civic Hybrid. It has two MPG readouts. One is an instant average and the other is current average like our trucks and it works the same way. My current average will read between 46 and 52, but when I hand calculate the tank overall it`s higher. It`s 55 MPG per tank. :-laf The average has nothing to do with per tank MPG. That`s the problem everyone is having and why they feel it`s out of wack.

 

[DrDiesel]

My experiance: (06)



The overhead gives you average MPG since the last reset.



The shorter a time since the last reset the more the current MPG affects the readout. IE: going down hill =65 MPG. uphill=13 MPG.



The longer a time since the last reset the less fluctuations you see on the readout since there is more "history" to take in to account.



Therefore: if you reset at fillup and do not reset untill next fill up you have (just before reset) the average MPG of the last tank full.



JMNSHO !

Yes... . That`s the key word... Average... . Oo.