sweetwaterguy

I have noticed my overhead estimate of my fuel economy is becoming less accurate. The first couple of years it was pretty close compared to hand calculating. Now it is consistently 1.5 to 2.5 off, reading higher on the overhead than actual mpg. Has anyone had a similar experience, and is there a fix for it?

Big Smoky

I have never trusted the over head console. I have never seen one that is real accurate. I also have 35" tires so I know its incorrect anyhow.

cdennyb

Another thing that needs to be kept in perspective...after all the finger pointing and snickering and calling names is done, is that overhead mileage computer calculates using a fixed set of constants. When you change injectors (like was mentioned above) that constant has now been changed and the calc is in error. The pumps, timing, chips, etc. all contribute to the calculation and changing or modifying any of those will create errors in the readout. i.e. changing injectors resulted in higher MPG's just as going the other way would change the readout the other direction.

Also, the mileage is calculated using miles travelled vs fuel left in the tank...so if you idle at the stop light for 5 minutes, watch the MPG drop. If the "running average" has been over the last 600 miles then it won't drop hardly at all, but if the "running average" has been for the last 10 miles, it'll drop several miles in a very short time.

If you fill up and hit the reset, and don't touch it until the next fill up, you will find it is very accurate, BUT... if you say, "Oh, I'm showing 23 on the overhead and I'm out cruising on the highway and getting 23 and hit the reset it'll be the same"...NO it won't. The previous readout was based on many variations of load, time, miles and fuel consumed and starting the overhead over by hitting the reset will begin a new set of calcs based on the upcoming variables.

If you fill up and hit the reset. Then go thru three stop lights just getting to the freeway and then look up when you get up to 60 mph, it'll probably read in the neighborhood of 10-15 mpg, but if you hit the reset and now measure your mileage over the next 50 miles of freeway, it'll be a more accurate representation of your cruising MPG. The first MPG of say 12 was based on you travelling say 1/2 to 3/4 of amile and sitting at the stop light for the 8 minutes or so. That initial 1/2 to 3/4 of a mile will not enter into the overall 50 mile calculation even though your fuel is gone! The bottom line is clarification... If I say I get 26-28 out crusing on the freeway at 55 mph...it means I hit the reset at that speed, allowed it to accumulate over a set mileage distance and without any stops or reasons to use excessive amounts of fuel, like passing someone, I was able to use fuel in an amount that gave me those mpg figures. It DOES NOT mean my truck gets 26-28 mpg all over town, hammering the throttle when I go thru underpasses to hear the stacks snort! LoL
It is very accurate, but only based on the constants and averages it figures.

So, for the most part. We ALL get lousy mileage 'playing' with our CTD's. That's a fact of life and ego. We also ALL will get better mileage if measured the same way and in the proper manner and realize that our variables are entering into the calculation every time we step on the throttle, either in the positiove or negative direction. So, unless you go into the ECM where the MPG calculation is stored and change the constants to match your situation of changes to the truck, you will never get an accurate mileage figure based on those changes. Keep in mind the result is based on miles travelled, amount of fuel used and the time it takes to get those miles. Less time, more fuel, same miles. More time, less fuel, same miles.
yes, it is really simple math but the playing fiel and the rules seem to change quite a bit from player to player.

db

hawkster

Mine is inaccurate from tank to tank resetting. Hand calculating is always 1.5-2 mpg less. Stock tires no tuner.

Donut Gestapo

I track and hand calc at each fill up. I reset everything at every fill up and run the tank near empty (last fill up was 33.4 gallons). I also fill the tank to the point I can see fuel in the filler neck (vent mod.).

My overhead is at least 1mpg to 2.5mpg high. Only once has it been low (0.6mpg).

I drive in the city more than on the highway. I have found that it is way closer the more highway driving I do.

Anyhow, it is a fun little gizmo to watch rather than the road in front of me.

Ramified5.9

I filled my tank to 34.6 gal It is supposed to be a 34 gallon tank right? (short bed) My fuel light as on and I was pretty low. Either the filler neck holds a lot of fuel or the service station was ripping me off!

hatchy

filler neck holds a lot.

kokalit

First, my overhead has always been off by 2-3 mpg since the day I drove it off the lot new with only 8 miles on the odometer. I have always hand calculated milage with all my vehicles.

Next, the "34 gallon" tank can actually hold 40 gallons (yes 40 GALLONS) filled to the top of the filler neck. The tank has an expansion hump which is filled with air on a stock tank and which I understand is to allow for gasoline expansion in hot weather. From I have learned on here the same tank is used in gas and diesel trucks. A tank vent relocation kit puts the vent at the back of the hump allowing use of that wasted space for fuel. Also makes filling up much much faster and wife doesn't have time to buy useless souvineers on long trips... The tank vent mod was the first one I did. But filling up from almost completely empty is much more painful now than it used to be. .

ptm600

I also reset everything every tank and hand calculate and compare. Mine is off 1.688 mpg since my truck was new. That is checking it over 1947 gallons of fuel, resetting it at every fill up. 80 of them to be exact, and it is always high by 1 - 2.5. So I agee with you 100%. They aren't accurate.

wreedCTD

Mine always read 2.5 high.

AH64ID

First, it uses injector pulse widths for calculations not fuel tank level.. thats just for DTE.

Mine has been anywhere from accurate to 10% off. But I have noticed that the more hwy I drive the closer it is, actually almost perfect and the more city its further off.. throw a small burt of towing in there and it has a hayday

coparam4x4

If I hand calculate when the pump shuts off, the overhead is spot on. Once I top off, then it's off.