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Discussion Starter #1
A random discussion for everyone. I know it’s generally accepted computer calculations are incorrect, but does anyone know why the computer per trip MPG calculation is terrible with the FFS? Is this a general Ford Fusion issue, did Ford not modify the calculation for the FFS differences or is this just an issue with mine, such as outdated firmware? Mine is a stock May 2017 build but I don’t know what IDS version number is installed for the various modules. I can’t assume the dealer maintained updates prior to selling.

I log this information but of course I didn’t buy the car for impressive MPG. I don’t care for underpowered average sedans, so this isn’t a complaint about low MPG. This of course is griping about a tiny feature that doesn’t impact the performance of the vehicle but if a feature exists, it should be reasonably accurate and consistent. I can drive the car easy or hard. I find the computer vs hand calc closer if I have a little fun with the car a few times throughout a tank of fuel.

Here are some previous fills, most recent to oldest. I reset trip 1 after each refill and run premium (93).
This most recent was a mix of city and 45-55 MPH roads without any goofing off and it’s the largest difference I’ve seen yet. Due to heavy Christmas traffic, average speed of 27.86 MPH though.
Considering how bad it is, the lifetime average isn’t too off at 17.7 MPG (computer 19.2).

16.5 MPG (computer 20.0) (what?)
18.7 MPG (computer 19.9)
17.6 MPG (computer 18.8)
17.8 MPG (computer 19.9)
18.3 MPG (computer 20.5)
18.1 MPG (computer 20.0)
16.9 MPG (computer 19.1)
24.0 MPG (computer 25.0)
17.5 MPG (computer 18.8)
17.5 MPG (computer 19.0)
16.7 MPG (computer 18.8)
16.7 MPG (computer 18.2)

My F-250 had an average of 99.7% accuracy with OEM tires (275/65-18) when new and is 0.2 MPG low (computer) with slightly larger tires (295/70-18) now so I know Ford knows how to dial in these computer reported calculations on some vehicles (computer is configured to 34.0” vs tire is 34.3”). My previous vehicles didn’t have a MPG screen and I don't pay much attention to rentals when traveling to know if other brands are better or worse.
 

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Mine usually is 1-1.5 MPG lower than what computer says.
My dodge diesel was the same way. My 14 mustang was 1 MPG
higher real world, vs computer (which was a nice surprise).

I've had some anomalies, but never pushing 4 MPG difference.
Mostly yours seems about what I get.
 

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16.5 MPG (computer 20.0) (what?)
18.7 MPG (computer 19.9)
17.6 MPG (computer 18.8)
17.8 MPG (computer 19.9)
18.3 MPG (computer 20.5)
18.1 MPG (computer 20.0)
16.9 MPG (computer 19.1)
24.0 MPG (computer 25.0)
17.5 MPG (computer 18.8)
17.5 MPG (computer 19.0)
16.7 MPG (computer 18.8)
16.7 MPG (computer 18.2)

My F-250 had an average of 99.7% accuracy ...
Excellent work.

Seems like the FS's computer accuracy is 92.2%, lol.
 

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Discussion Starter #5
Since this post I accidentally used trip B for two tanks in mid January. One was spot on at 18.9 both computer and hand calc. I thought I was on to something (programming error with screen A). However, the second one erased that idea at 19.2 computer and 17.7 hand calc.



I can't explain the 16.5/20 but that is the only time and was the 20th tank.



So far lifetime average is 17.7 hand calc on 93.
 

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With only a few tanks on our FFS, I’ve observed about a 0.25 MPG difference, with the computer being optimistic. I do only fill the tank to the initial pump shutoff, and do not try to “top her off”.
 

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Mine had always been about 1-1.5 high on the computer.
 

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I found mine was pretty accurate over a full tank. Accuracy decreased a bit on half tank fill ups.

How much do you have the car warming up on remote start? This would impact your hand calculations.

Without having actually tested the theory, it is possible that the computer is measuring in metric and the error comes about in the conversion to imperial. Fusion is originally European. It is possible all of the sensors were calibrated in SI (metric) and the conversion math doesn't have enough decimal places for accuracy.

Had a similar issue with measuring flow rates of pumps in a previous life and ended up discovering the number of decimal places in the flow meter to convert to US units was insufficient and impacted the accuracy.

This can present as an issue as the flow meter is likely measuring something like millilitres per second so the multiplication needs around 8 to 10 decimal places to go from metric to gallons with a degree of accuracy. Betting the software doesn't go beyond 6 decimal places. Likely 5, which is what we found out from the flow meter manufacturer.

Worth noting that the sampling rate and averaging by the computer is fairly archaic. I've been in friends beamers and audis and their fuel efficiency is shown in real time. On ours the averaging calculation is so slow that it takes about 15 minutes or so before the number plateaus out to something close to what you are consuming after a reset. Even at constant speed. Do a reset while you have cruise on to see what I mean.

Just a theory and some babbling out loud.
You've got me intrigued enough to start keeping the gas receipts again and resetting the trip computer. I am interested to see whether it's still close. Just realized that I work in litres/100km which would mean I wouldn't see the difference (error) as much. I'll do my calc's in both units as I might have the same error, just haven't noticed.
Thanks for posting your numbers.

Just did the math. Conversion error is only going to be about 0.1% in our case. Bit of a waste of the readers time-sorry
 

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Discussion Starter #9 (Edited)
No issue with out loud babbling, I do it to. Just good (random) discussions.

I remote start I'll guess 60% of the time while approaching the car. 1.5 MPG would be a decent amount of idling though. However, that is a good point because I'm not sure the computer is logging the trip A/B info until accessory power up. I have not considered this.

< 30 seconds to finish approaching, +30-60 seconds to get situated, seat belt and maybe open Spotify when it doesn't start playing half the time on its own.
I've started at least 12 times over three days this week and at least six I know were push button. No idea for the rest of the tank and need to fuel tomorrow.
I now need to avoid remote starting for a few tanks but I don't know if I can achieve that... LOL.

Does anyone know the series of buttons to press between KOEO to KOER to get the dash into engineering mode? I want to see my running vs idle hours now.
I thought it was hold right OK at start. I tried from off and from accessory mode. I'll check the university of Google and retry later.
I have no reason for keeping up with MPG details other than I just like the data.

Edit: Holding left OK button at start is engineering mode. No idle hours though.
 

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I just got gas today and checked this. Computer said 23.3, actual mileage was 21.9 mpg.
 

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One thing that I thought of is the simple fact that this is the accuracy variance of the sensors. Guessing they are mass produced cheapies with some degree of accuracy drift outside what we are hoping for.
I'm guessing the gas pump is relatively accurate so most of the error is likely in the car sensors. In Canada the gas pumps have to be calibrated, so they will be pretty spot on.

Last random thought is that there may be a volumetric difference between winter and summer temperatures of the fuel. I can't remember which way around someone told me but I think it was that you got slightly more fuel than the pump measures in winter over summer. May be a bit of urban legend as I have never bothered to pull out the old text books to verify or do any math to see whether any difference would be meaningful.

It's Friday. Brain hurts. Beer calling.
 

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You can enter the Engineering Test Mode and adjust the AFE Bias to better correct the calculated fuel economy in the computer. I take actual fuel readings and the computer readings for each fillup, so I Have a good sampling size. My AFE bias is roughly 0.945 (multiply computer reading by 0.945 to yield actual) on average.

Just curious what others are getting with their FSport.
I'm averaging 21 mpg with 50/50 mixed driving, and if I do 100% highway, it is 29 mpg. This is with my latest tune.

Just as a comparison, my Explorer XLT AWD with the N/A 3.5 V6 gets 20 mpg average in the same driving schedule, and 26 mpg with 100% highway.
 

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You can enter the Engineering Test Mode and adjust the AFE Bias to better correct the calculated fuel economy in the computer. I take actual fuel readings and the computer readings for each fillup, so I Have a good sampling size. My AFE bias is roughly 0.945 (multiply computer reading by 0.945 to yield actual) on average.

Just curious what others are getting with their FSport.
I'm averaging 21 mpg with 50/50 mixed driving, and if I do 100% highway, it is 29 mpg. This is with my latest tune.

Just as a comparison, my Explorer XLT AWD with the N/A 3.5 V6 gets 20 mpg average in the same driving schedule, and 26 mpg with 100% highway.
How do you get to and adjust that? My average at 26k miles is still 1-1.5 high on the computer.
 

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How do you get to and adjust that? My average at 26k miles is still 1-1.5 high on the computer.

My FSport is off a lot more than the Explorer. With the ignition off, hold the OK button on the left steering wheel control. Turn on the engine/accessory power (don't start engine) and keep holding OK until "ET" pops up on the left MFD display. Scroll up to find AFE Bias and use Left/Right to adjust it.


I was told the AFE Bias of 1000 means 1.000, so when you divide your actual MPG by the computer MPG, you should get a smaller number (say you calculate 19 mpg but the computer says 20 mpg, then it is 0.95). I recommend a large sampling size and averaging out these differences, and change the AFE Bias to that number (0.95 would be 950). Hit Ok, and shut off the car. I was also told that it takes a few fillups for this change to take effect. If you do a search on Google, you should find a lot of other Ford forums doing the same thing for their respective platforms (Focus, Mustang, F-series, etc...)
 

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I put 14.418 gallons in it, 402.8 miles = 27.93 mpg's calculated

I'm running one of Torrie's MPG tunes, on the second revision.

I really don't like this gas gauge, numbers don't add up, distance to empty said like 40, but I only put 14.4 gallons in it.
If we have an 18 gallon tank there's a large error in the calculations.
 

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I really don't like this gas gauge, numbers don't add up, distance to empty said like 40, but I only put 14.4 gallons in it.
If we have an 18 gallon tank there's a large error in the calculations.
The DTE and fuel gauge does not account for the reserve fuel. Ford tends to leave at minimum 1 gallon as reserve. My CD3 Edge Sport tends to leave almost 2 gallons at 0 miles DTE, for example. Plus the DTE doesn't go off your current average. If you reset the average on screen, it still starts calculating the DTE using a pre-learned overall average.

14.4 gallons added
+1.5gal reserve (estimate)
+40mi to E @ 20MPG = 2 gallons.
Total 18 gallons.
 

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I put 14.418 gallons in it, 402.8 miles = 27.93 mpg's calculated

I'm running one of Torrie's MPG tunes, on the second revision.

I really don't like this gas gauge, numbers don't add up, distance to empty said like 40, but I only put 14.4 gallons in it.
If we have an 18 gallon tank there's a large error in the calculations.

Just curious - what is your drive schedule? Was that 100% highway?
 

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This tank was probably 90% highway, but after I got back from my trip the MPG's didn't go down any with my 2 day work
commute. I was hauling a$$ down to Columbus too, at least 80 mph the whole way, I was actually shocked I pulled in at 29 and at one point it flashed 30 on the way down, it dropped when I pulled into the parking garage.
I was guessing I had a tail wind the whole way.
 
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