I realize that this has been covered before and that there is a definite variance in speedos,but I have found something I find odd...

My speedo when checked against a GPS unit shows the speed to be accurate to within 1%. However, the trip meter is off by about 4%.

Of course this fact, combined with the "fuel used" item on the computer being quite inaccurate leads to generous readings on the lie-o-meter.

Anyway, does anyone else notice a difference between speedo and trip meter or are they consistent with each other? I thought they use the same sensors and therefore should be consistent with each other?

 

You pose an interesting question. I wonder if the odometer and trip meter get their information from the same source as the speedometer. You would think so, but I have learned to expect the unexpected with this vehicle.

 

I had guessed mileage was calculated from the MPH reported by the computer vs. the speedometer. If you put your truck in engineering mode, you'll see the MPH reported on the screen is lower than the guage. My screen reports a more accurate speed with my GPS than the guage does. Basically, I have three different speeds.
My Garmin topo GPS also reports the same speed as my Garmin road GPS at steady speed (GPS have a second or two lag time).

 

What's this "engineering mode" you speak of?

 

It has been reported that the conversion factors for liters and imperial gallons have a programming error issue. The Ford engineer that has posted here several times has sent an inquiry up the engineering chain.

 

Hey Great Danes - I previously posted about a potential mileage/fuel consumption calculation issue on the Canadian trucks. In my truck my fuel used calc is consistently 18 to 20% less than what the pump is reporting to me. Most of the US owners are reporting accuracy of 2% or less. Interestingly, if I reverse the calculation using imperial gallon conversion rather than US gallon conversion, I can make up the difference. In other words, I can get to within 2% of my lie-o-meter reading by the following formula:

Lie-O-Meter = Pump litres filled / 4.54 Imperial Gallons* 3.78 US gallons

Could be coincidence (or just my truck) but regardless the difference of 18-20% is way out of spec. Maybe you can try out this calc next time you fill up and see if you get similar results.

In any case, PowerstrokeHD has asked one of the Ford engineers about the calculation algorithm so hopefully that will shed some light.

 

Ricatic beat me to it!

 

Check out this topic, thanks to rdenis.
https://www.ford-trucks.com/forums/1...test-mode.html

I don't think anything can be changed in that mode but don't try...haha!

You have to put it in to this mode before starting.
The first test is the guage test then you can start it (before the fuel pump shuts off).

I may start testing the GPS miles vs. truck computer miles travled. I have not put any effort into that part.

 

OK, so I ran the truck in "Test Mode" and the digital speedo was about 4% slower than the analog dial, which was the same as my GPS unit. This seems to indicate that the odometer is based on the digital speedo since it is also low by 4%, which in turn would suggest that there are different sensors for distance and speed.

I haven't filled up yet to confirm the mileage calculation using imperial gallons vs US gallons and litres.

 

Two Factors play against you using GPS 1. The Government does not allow the GPS to get correct geo data to pin point your exact location. 2. Latency of the data packet with geo data which takes about 1 sec up to the satellite and 1 second to return to the GPS. This makes your GPS a little lose in the data you see.

 

I understand the GPS data issue, but what I meant to say was that the GPS and the analog speedo match each other and the digital speedo (Test mode) and the odometer are both 4% low compared to the other two.

 

1. The feds have not used selective availabilty (SA) since the first Gulf war. Your GPS can be as accurate as the unit is made to be.

2. The GPS is a receiver, not a transmitter. One way data stream and far faster then 1 second.
Most consumer GPS units do have a 1 or 2 second update average to keep the reading steady.

 

I don't want to pretend to know the answer to your questions, but have checked mine on several occasions. On a 200 stretch (per the mile markers) on I-10 my odometer logged 193 miles. So I know it is reading roughly 3.5% low. I also checked my MPH at various speeds against a GPS and two fixed (sign mounted) radar detectors, the difference was that actual speed always lower than the analog MPH indicator -- but it was speed dependent -- not a consistent percentage difference. I will try to make some time today to dig the numbers up on a prior post if you think that it would help you find the answers.

Epic Cowlick (I think) posted that there may be a regulatory mandate concerning the MPH reading on the speedometer. I think that, because of this regulation, the manufacturers make speedometer read high. I interpreted it as a means to avoid people getting speeding tickets and being able to claim that the speedometer is reading too low or is "off".

Since I don't drive in engineering mode I can't be of much help in that respect, but have put my mind to rest concerning the issue because the difference, in my case, is just too small to worry about. The newly found bounce in the right front tire after a rotation is a different matter.

 

Well , I finally got around to filling up the truck again, and I performed the conversion as noted and my lie-o-meter is within 4% of the calculated result as opposed to being out by 15%. There is definitely something going on with the algorithm in the Canadian trucks...

PowerstrokeHD, any further insight?