When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I'm still tracking my actual versus indicated, and there is some good news/bad news.
In the good news department, the average percent error is actually getting smaller as the truck has been getting broken in. My original error percentage was ~~ 7%, and then it seemed to be settling into ~~ 5%.
However, the average error is now approaching ~~ 4% (note the downward slope in the average line in the graph below).
In the bad news department, the variability is getting worse. It now varies between 2% error (not too bad actually) to as much as 6%. So whatever mechanism Ford is using to determine fuel usage, there appears to be quite a bit of variability in the actual value.
Well guys. I took Kahuna in for its 12K mile service. In addition to the usual, I also had them apply the TSB for the harsh 5->4 downshift, and requested that they adjust the MPG display. They refused, and came back with this from Ford corporate (excuse any typos, I transcribed it from the service report):
The vehicle's MPG reading is functioning normally and there are no adjustments available to alter the MPG reading. There are various factors provided into calculating the vehicle's MPG reading that will alter what the cluster displays. For one example, the vehicle is designed to display the vehicle speed based on wheel sensors. If the vehicle tires are worn the vehicle speed will read faster than the vehicle is actually moving due to the decreased circumference of the outside tire diameter causing the wheels to travel less in one full rotation. This little bit of tire wear will influence the mile per gallon reading just like environmental factors and vehicle operating characteristics will influence this reading. The miles per gallon cannot possibly be 100% accurate as there are several factors going into this calculation. Advise the customer this is a normal characteristic of the vehicle and no repair is required.
So they claim that just the tire diameter will affect this reading. I think this is bogus, as the miles traveled by the vehicle are the same regardless of whether the mileage is hand calculated or used by the cluster. Am I wrong on that count?
If I can get my hands on a diagnostic plug-in, I will start messing with the AFE BIAS on my own to see what happens.
The tire size does change the MPG calculation. But, since you are probably using the truck's odometer to do the hand calc and the truck uses the same number to do its calc, when the two MPG calc's differ it cannot be because of tire size.
The tire size does change the MPG calculation. But, since you are probably using the truck's odometer to do the hand calc and the truck uses the same number to do its calc, when the two MPG calc's differ it cannot be because of tire size.
Please let us know how your mod's go.
Exactly my thought process. Since both the cluster and the hand calculation are using the same "mileage" numbers (regardless of whether they are high, low, or correct), they should come up with the same number. The issue is how much fuel is going into the engine, and how it is measured (or not).
I agree that the hand and cluster calculations should be closer, but I think the important thing to note (and I have noted in previous posts, possibly in another thread) is,
"...environmental factors and vehicle operating characteristics will influence this reading. The miles per gallon cannot possibly be 100% accurate as there are several factors going into this calculation...."
Don't get me wrong, I think the factory calculation should be better 'averaged' for all these factors and I don't like seeing the difference in MPGs, but I think you are going to be constantly adjusting the computer.
I agree that the hand and cluster calculations should be closer, but I think the important thing to note (and I have noted in previous posts, possibly in another thread) is,
"...environmental factors and vehicle operating characteristics will influence this reading. The miles per gallon cannot possibly be 100% accurate as there are several factors going into this calculation...."
Don't get me wrong, I think the factory calculation should be better 'averaged' for all these factors and I don't like seeing the difference in MPGs, but I think you are going to be constantly adjusting the computer.
I disagree. The computer knows quite precisely how much fuel it is injecting into the system from the pump pressure and the pulse width to the injectors. And it knows how far you drive. So, simple math, without enironmental factors and operating conditions, gives MPG.
However, I do agree that the accumulative effect of tiny errors in fuel flow multiplied by the millions of pulses in a drive that uses a tank of gas can cause errors. But, I find it quite curious that all of the errors I've seen reported have been on the optimistic side. ALL.
In any event, if there is a way to tweek the calculation I'm in. I think we can zero in on accurate results.
In the bad news department, the variability is getting worse.
I would think that much of the variability is due to the accuracy of the hand calculations.
From one tankful to the next, how do we know just how full the tank is? I mean the vehicle would have to be parked at the exact same angle as the previous fill. With the same load. With the same nozzle (not too fast, not too touchy, etc). Maybe using the same pump each time would minimize some of the hand variables.
Might be interesting calculating the difference over a couple 1000 miles and see how much they differ.
I disagree. The computer knows quite precisely how much fuel it is injecting into the system from the pump pressure and the pulse width to the injectors. And it knows how far you drive. So, simple math, without enironmental factors and operating conditions, gives MPG.
However, I do agree that the accumulative effect of tiny errors in fuel flow multiplied by the millions of pulses in a drive that uses a tank of gas can cause errors. But, I find it quite curious that all of the errors I've seen reported have been on the optimistic side. ALL.
In any event, if there is a way to tweek the calculation I'm in. I think we can zero in on accurate results.
Had there been a Debate Team for me to ever have been on during my life I would have been terrible. Often times I reread/rethink my arguments and can't find the point or realize it is poorly made.
My point is in agreement with you but seems to rarely be considered in every MPG discussion I have ever read. There are so many things going on that even the smallest error in half of them can accumulate into the final error that we determine is unacceptable. As far as all the errors being optimistic, I can't explain. My GUESS is the computer is programmed on a dyno in close to perfect conditions, but again that is a guess and I am terrible at guessing. "All good sailors go to 'C'", right????
Anyway, Cheers all and after a long absence from the forums, I am back to reading again. I am interested in seeing if the computer can in fact be reprogrammed to provide accurate MPGs.
I would think that you would have to use a stand alone GPS, or drive a route based on mile markers. The odometer, as already stated, is in accurate. There are too many variables to get a consistently accurate odometer reading. Just starting out with cold tires and then having the pressure change 5-7 PSI while driving will cause a measurable effect.
The computer knows quite precisely how much fuel it is injecting into the system from the pump pressure and the pulse width to the injectors. And it knows how far you drive. So, simple math, without environmental factors and operating conditions, gives MPG.
There are only two variables involved in calculating MPG; miles and gallons. If the hand calculation and the cluster are using the same miles, then the only difference is the gallons.
Further, based on what I've seen on this forum, almost all the trucks are fairly consistent with about a 5% error. That should be an easy fix.
There are only two variables involved in calculating MPG; miles and gallons. If the hand calculation and the cluster are using the same miles, then the only difference is the gallons.
Further, based on what I've seen on this forum, almost all the trucks are fairly consistent with about a 5% error. That should be an easy fix.
Amen! But, doesn't want to fix it. Why should they? We have lots of people on here quoting what the LoM says for what MPG they are getting. So is getting the benefit of the optimistic #'s and has no reason to fix them.
04-11-2016, 03:29 PM
doesn't want to fix it. Why should they? We have lots of people on here quoting what the LoM says for what MPG they are getting. So