overhead fuel miles

[skorski]

I went to the dealer today to have the injector pump replaced and have the overhead fuel miles recalibrated. They said it was off because of the leaky pump. . Try it with the new on. I don't beleive them . Has anyone had theie overhead redone to match hand cal. And can this even be done. Lot of money for something that don't work.

 

[BHaden]

Good timing. I just was going to ask the same question. Mine is consistently about 2mpg higher than hand calc. It has varied from 1. 6-2. 2 off. Kinda PITA. My previous '03 4. 7 was always 1-1. 5 off. My wife's 05 Liberty 3. 7 is always within a tenth or two of correct. Why can't DC make them all closer? Is it just a big truck problem?

 

[Prairie Dog]

There's no way to recalibrate it and unfortunatley, it's normal for them to be off just as you both have experienced.



Scotty

 

[JHardwick]

You can get a feel if you hand calculate long runs. The overhead is never gonna be completely accurate, but you can still get a feel after calculating a few 2-3 tank runs.

 

[TowPro]

I find the 2nd gen trucks showed the average since the last time you reset the overhead to 0. the 3rd gen's seem to show the average over the last 50-100 miles.



If you run it hard for 300 miles, then take it easy for 100, the display is going to read much higher then hand caculated. I find mine is pretty close when I drove the same road every day to work and back and don't go anywhere anything different.



I also find mine is close over the road towing.

 

[DPKetchum]

The times I've checked mine its withen . 5

 

[Big P]

If I keep the truck on just the highway cruising the same speed for an extended trip, it will be within . 1-. 3 tenths.

 

[JWChessell]

I just started logging the computer readout versus the hand-calculated mileage on 9-12-06. Here are the last three tanks, all pulling a 16' 2-axle fully-enclosed trailer weighing 2840 lbs empty:



512 miles, cruise-control at 64 mph, computer = 13. 9, hand-calc = 13. 364.

387 miles, cruise-control at 64 mph, computer = 12. 7, hand-calc = 12. 152

413 miles, cruise-control at 63 mph, computer = 13. 7, hand-calc = 13. 135



That's a fairly consistent error of . 536, . 548 and . 565 mpg, w/an avg of . 550.



Avg computer reading for those three tanks was 13. 433; avg hand-calc mileage was 12. 884 -- using averages the average discrepancy for all three tanks of fuel, between the computer and the hand-calc was . 459 mpg.



So in my case, both the actual and the average discrepancy between the mileage computer and hand-calculations was approximately 1/2 mile-per-gallon, +/- a few hundredths.

 

[LFJ]

I just started logging the computer readout versus the hand-calculated mileage on 9-12-06. Here are the last three tanks, all pulling a 16' 2-axle fully-enclosed trailer weighing 2840 lbs empty:



512 miles, cruise-control at 64 mph, computer = 13. 9, hand-calc = 13. 364.

387 miles, cruise-control at 64 mph, computer = 12. 7, hand-calc = 12. 152

413 miles, cruise-control at 63 mph, computer = 13. 7, hand-calc = 13. 135



That's a fairly consistent error of . 536, . 548 and . 565 mpg, w/an avg of . 550.



Avg computer reading for those three tanks was 13. 433; avg hand-calc mileage was 12. 884 -- using averages the average discrepancy for all three tanks of fuel, between the computer and the hand-calc was . 459 mpg.



So in my case, both the actual and the average discrepancy between the mileage computer and hand-calculations was approximately 1/2 mile-per-gallon, +/- a few hundredths.

Why would you pull a trailer around for three tanks of fuel just to check the mileage? You said that the trailer was empty? Just wondering.

 

[sag2]

Remember that thing is doing it's calculation by keeping track of the theoretical flow of the injector, and then keeping track of the pulse width of the injector and the fuel pressure at the time of the injection event. I'd say based on the size of the orifice in the injector, and the length of the injection event, being within a mile or two per gallon is pretty darn good.

 

[skorski]

overhead fuel miles.

Thank you for the input. I still think if they are going to offer something it should work. They indicated to me that it could be recalabrated, so maybe I'll play along with their silly game and keep bringing it back. Ski

 

[JHardwick]

Why would you pull a trailer around for three tanks of fuel just to check the mileage? You said that the trailer was empty? Just wondering.

He didn't say it was empty.

 

[Dieselnerd]

Mine has always been very close to hand calc. I do reset it with every tank. If you seldom reset the error grows larger. I find it to be a useful tool to see the difference in mileage with headwind, towing, etc. I also find it useful to see how many miles to empty when out in the back country. I know it will always go at least that far. Gives me a little peace of mind.



I don't expect it to be 100% accurate. There are too many variables.

 

[MoparBob]

I have found mine to be pretty close and I reset it with each tank refill. I don't rely on it for 100% of anything, but it is a nice tool to use to gauge driving habits and how I am doing with fuel economy at certain speeds and under certain loads.

 

[jersey diesel]

overhead

mine is constantly under by 1. 3 to 1. 6. Dealer said thy would check it. That was awhile ago: nothing was done and I didn't push it just in case they had to mess with ECM to correct it.

 

[JWChessell]

LFJ; JHardwick:



I'm hauling our household stuff from so. Calif to our retirement home in Washington State. Loaded going north, empty coming south. 4 round-trips so far, probably 2 to go. I've tried to find paying loads for the south-bound trips, but so far nothing compatible with the trailer and where I'm going.



I've kept mileage records in general and more involved ones for these trips, as I'm experimenting with a wind deflector I made, trying to find the best angle for least wind resistance and still get the wind up over the trailer. It wasn't until coming south on the last trip (early Sept. ) that I started logging the mileage indicated by the computer alongside the hand-calc mileage. Two of my regular fuel stops are 512 miles apart, and at around 13. 5 MPG that only leaves me a reserve of slightly less than 2 gallons of fuel. Knowing the average error in the MPG computer will let me know if I need to get fuel sooner than planned.

 

[sag2]

Don't waste your time going in for them to "calibrate it" as there is nothing to calibrate. WYSIWYG

 

[Jack in Alaska]

On my truck hand calc. is 1. 5 to 2. 0 lower than the overhead.

My Chrysler 300C is almost spot on both methods.