Average Fuel Economy Readout PROBLEM

[Yo Hoot]

All of a sudden I'm reading under 13 mpg all the time. Truck runs perfect and I see no unusual drop in fuel/driving.



I haven't done a hand calc yet but noticed when sitting at a red light mileage drops . 1 about every 30 seconds. Didn't used to do that.



Something is goofy here.



Could it be a faulty sender? Fuel gauge seems to be reading fine.

 

[JThacker]

Hey man my overhead computer has been calculating 16. 6 and 17. 1 mpg on my two tanks but by very accurate hand calculations I have gotten 14. 7 and even 22!!!! The computer can't do math.

 

[rbattelle]

I reset my overhead after every fillup, and it almost never reads correctly. For example, the last tankful was 19. 8 mpg and when I stopped at the pump the overhead read 17. 9.



Having said that, I've never seen more than 2-3 MPG difference between actual mileage and overhead mileage. Do you track your mileage at each fillup?

 

[Yo Hoot]

No I don't do every fill up. But it won't go over 13 at all. Always did before. I restet it and after 5 or 10 miles will not go over 13. Did before.



Why would the mileage show a continuous drop while sitting at a red light? Didn't do that before either. I think somethings wrong with the computer or it's inputs. I will calculate by hand for a while to prove it wrong.

 

[John - K5AWO]

You don't want to do the reset on every tank. The computer does an averaging on a history basis.



When it gets reset, it has to start from scratch and small variances in the way you drive will cause large calculation errors. Give it a chance to learn your way of driving and don't reset it.



The instantaneous, if you have one, should pretty much be okay all the time. But the averaging part, don't reset it.



Experience here on that one...



Do a reset at the top of a hill and watch the display. Reads way high. Likewise, reset at the bottom of a hill. Climb the hill under accelleration all the time. Doesn't take much throttle, just so it keeps trying to gain speed. The avg mpg will hit the tank.



Takes an average over time to give you anything meaningful. No less that how we have to do a hand calculation. Do it on little trips and your accuracy is not good. Do it over 3-5 tanks of fuel, you get a truer average.

 

[DKizerian]

Originally posted by Yo Hoot



Why would the mileage show a continuous drop while sitting at a red light? Didn't do that before either. I think somethings wrong with the computer or it's inputs. I will calculate by hand for a while to prove it wrong.

When you're sitting at a red light, your truck is using fuel and going absolutely nowhere... if you sat there long enough you'd run out of fuel and have ZERO miles per gallon... if you just reset your mileage computer it is WAY more prone to show these otherwise minor drops and rises...

 

[Yo Hoot]

Originally posted by DKizerian

When you're sitting at a red light, your truck is using fuel and going absolutely nowhere... if you sat there long enough you'd run out of fuel and have ZERO miles per gallon... if you just reset your mileage computer it is WAY more prone to show these otherwise minor drops and rises...

Yes I know but it didn't change like it is now, before. Not . 1 every 15 or 20 seconds. Does yours?

 

[Badunit]

The only time mine will decrease that quickly is when sitting at a light or going up a hill within a few miles of resetting the computer. But that makes sense. Yours reading low doesn't make sense and if it is decreasing at the rate you indicated even after 50 miles or so it shouldn't be.

 

[Badunit]

How about trying a diagnostic test on the console. It probably won't tell you anything but it's worth a shot and might clear it up. Here's the procedure from the service manual:



Turn ignition off

Press and hold STEP and RESET

Turn ignition on





I haven't tried this on mine but that's what the manual says to do.

 

[CAgnoli]

My truck overhead will go down . 1 miles per gallon if the truck is at idle for 20 or more minutes, never at a red light.



As for resetting the computer, I reset mine at every fill up, and it's within . 4 mpg every time. To be fair, I drive the same 186 miles to work and back every day, on the same road, with the cruise control, and no towing, so the computer doesn't really have that much to learn



Just turned 15k on the odometer today, had the dealer service the transmission, rear end, change the oil, rotate the tires, and empty the water filter, change the fuel filter. $374 out the door. Now I don't have to touch the truck for 15k miles. (I'm adopting the 15k oil change interval since I don't tow, idle the truck, or drive anything but 4 lane highways at 70MPH.



(Dealer approved it... . we'll see if I have a warranty issue down the road, probably should get that in writing..... )



C-ya

 

[DKizerian]

when I first reset mine I drive about 3/4 of a mile before hitting a very long red light, and at this light I can watch it drop from 9-10 down to as low as 6-7 rather quickly... . but the rate at which it is dropping slows way down as you get over 40-50 miles since the reset...



maybe take it to the dealer after you've gone through a whole tank and have verified that either A) the overhead is grossly incorrect, or B) the mileage has dropped substantially



Good luck!

D

 

[Yo Hoot]

Thanks everybody for the great responses. I did the key on two button reset last night. It "PASSED". Don't know if that will make any difference. I've got 8000 miles on the truck. For the first 7900 miles I could reset it and once all things settled it would climb fairly quickly on a slow highway run... up to 17 and then poke it's way up to 19+



Now it never goes over 13-14 on the highway. Wierd. It shows such a downward tendancy. Takes a mile to go up . 1 but drops . 1 every 20 seconds when I stop.



I'll be fueling up probably today and won't use up the tank till next week unless I do some surf fishing before then.

 

[DHalbrooks]

Same Thing

Having the same problem Just got back from long weekend dip netting in Alaska and drove 1000 miles, computer never ead anything above 16. 5 MPG. Hand cals down were 17. 6MPG and return were17. 5MPG.



Who knows, love the truck. Better to be off lower than higher.

 

[Yo Hoot]

Looks like reset did the trick! More later

 

[rbattelle]

Originally posted by John - K5AWO

You don't want to do the reset on every tank. The computer does an averaging on a history basis.



When it gets reset, it has to start from scratch and small variances in the way you drive will cause large calculation errors. Give it a chance to learn your way of driving and don't reset it.

The whole point of resetting at every tankfull (for me, anyways) is to get an average fuel consumption for that specific tankfull. I do lifetime averaging myself. BTW, since new (65 fillups and 1600 gallons of diesel burned), my average is 18. 6. About 60/40 highway/city.

 

[radar doctor]

Fuel Mileage

Mr RB, are you driving a 4X4 or 4X2??? I drive a 4X2 03 and that is near what i get, I have a overall figure in a few days. Have a great Day. Raining here... Doc

 

[rbattelle]

Mine is a 4x4. I'm surprised your mileage it not a little better than mine. Then again, there are some people who drive the same truck as me and claim 21 mpg. I do drive quite conservatively most of the time (to the point that my friends complain that I drive too slow).

 

[Yo Hoot]

The reset I'm talking about is the "Test" reset that was mentioned earlier. Yes, I realize you need to use the normal reset often because the total average will keep coming down. Read the whole topic and you will see what was happening to me.



I did the BIG reset. Turn key on while holding reset and step.



I confirmed tonight that it's back to normal for sure. Also whole cruising 65 on the highway, I reset to zero. After a few miles she settled on 20+ mpg. Wavering between 20 and 20. 5. I'm quite happy with the mileage I'm getting except around town could be better.



Badunit..... thanks!

 

[Badunit]

I'm glad it worked for you.

 

[RKerner]

Constipated overhead?

After my last fill and calculating 16. 9mpg highway (AC on) with the overhead at 15. 3mpg, I did the hard reset. On the way back to the house, I saw 17. 0mpg :--)which is the highest number I have ever seen out of the overhead. The previous max was 16. 2 on the overhead with a calculated 18. 0. Now if I can just stop from losing one mpg for having the AC on, I would damn near be happy with this thing. Oo.