Scangauge Comparison

[GaryG]

Just did a comparison of the Scangauge tank MPG average and the FEH Navi 15min MPG average and found some interesting results. Both were reset at my last fill up, and I monitored them both for 579 miles very close till today’s fill up. This tank was a mix of driving, generally city up to 55mph.

Today, I had about 25 miles of poor mileage and 25 miles of 60+ mileage. The scangauge tank average had settled in around 45.6 MPG after 500 miles. The Navi bounced around to 46.4 MPG when I got the SG up to 45.8 MPG tank average. What was happening was the Navi 15min average would increase the average MPG faster than the SG when I was hitting top MPG. This morning was a bad segment and I reduced my SG tank reading to 45.1 MPG average. The Navi dropped to 44.6 during the poor 25 mile segment, .5mpg less than the reading on the SG. At this point, I made my way over to the beach roads to raise my average on my return home. Got the FEH in the upper 60's, but the heat must have reduced my battery’s ability today because there was no way to get her to 80mpg, which I had hope to hit today.

Since I had about 70 MTE, I decided to fill up near my home and take the final readings on all the gauges. Here is the results after 25 miles of final 60+ mpg trip.

Scangauge

Tank average - 45.9
Gallons used - 12.5
Tank miles 572

Navi 15min MPG average -47.9
Pumped 12.8 gallons
FEH Trip reading - 579.6

If I go by the data on the SG tank miles (572) and divide the gallons used (12.5) I got 45.76mpg, not 45.9 that it read.

If I go by the 47.9 MPG 15min average, you can see it is off because of the last 25 miles of 60+ MPG. If I divide the 12.5 SG gas used into the 579.6 FEH Trip, I get 46.368 average Tank MPG.

The point that needs to be made is the 15 min average has a shorter data savings memory than the SG tank average. The gauges stayed within .3 MPG till I started getting poor (less than 45 MPG), and then 60+ MPG. But based on my knowledge and experience, both gauges would settle back to within .3 MPG.

For some stupid reason, I grab the 93 octane (for the first time) instead of the 87 octane Sunoco nozzle, and filled my tank. If 93 octane has ethanol in it, I’m screwed. Has anyone done this and had a problem with mileage? Well, I guess this will be another update issue for me in the near future.

How does the SG compare in your vehicle?

GaryG

[tbaleno]

Nice information there. Yeah. you set your self up for another post if you put in the 93 octane

[VietVet'67]

Gary and John –

Now you both have me really confused – not really!

Since I don’t have the ScanGuage I have only the NAV display (the avg. line) to go by. I reset it at every fill-up and have been using that reading for my post etc. I know that there are many variables that come into play when using the gallons of fuel pumped divided by the miles driven (shown on the odometer) – at least for one single tank.
I would think that for a long average – say 2K miles (or your total distance since recording) divided by the fuel pumped over that time/distance would average out to give a pretty accurate reading on your overall MPG. So I am going to take my actual miles (about 10K) and add up the fuel pumped for that distance and see just how close ‘That’ average comes to averaging all my ‘single’ tank MPGs.

The one main thing I can think that would make a big difference, is the accuracy/calibration of the odometer, no matter if it is a manual average, ScanGuage or NAV average. I would think that both the NAV and ScanGuage use the same OBD numbers of fuel going thru the system – and I would think that this reading is pretty accurate.


John – on the 2,000 data point thing. I would have to think that the one per minute that you suggested, as used by the 15 min graph would be wrong. Think about it – if you watch the reading it goes up and down at the blink of an eye. Example: I will lose about 0.3MPG just getting out of my drive (100 yds and up hill) – but it only takes 30 seconds and that display is dropping say 34.9, 34.8, 34.7 in that short period. So before I got out of my sub-division I would have used up my 2K data points.

Now I am confused.

[GaryG]

Phillip,

Your a sharp guy. The data is dropped off the Navi 15 min average between the time I last filled up for sure. So, if my average speed was 20 mph (averaged from the start of the FEH till shut off) and I went 579.6 miles, it would have taken about 29 hours of driving. John's suggestion is that the 15 min average has 2,000 data points (which John thinks are minutes) that equals 33.33 hours. While the data I am using comes from the SG, that's close (29 VS 33 hours).

The two gauges have been close, but when I saw this change in the 15 min average, I knew there was a point when the 15 min average could start becoming off. You must take into consideration the time and average MPH I drove. My guess is, no one reading this thread drives in EV as much as I do. Therefore, until FEH owner's with the Navi start driving the way I get across town, I think the 15 min average is just fine giving the correct average tank at fill up. It is obvious, Ford spec the Navi with lower MPG estimates then what some of us are hitting. At this point, I will monitor the 15 min with the scangauge to find how many minutes of data it stores. We now know it will not store all of a tank for me with the A/C off most of the time. My guess is that the amount of Tank hours on the scangauge when the 15 min start dropping data is around 25 hours. Maybe the hours are off, and 25 = 33.33 or something. Also, I use "N" to park and stay in EV at stoplights, draw bridges, waiting for my wife for lunch etc. to keep the ICE off. This time maynot be counted by the SG because the ICE is not running. The clock may be adding data to the Navi that the SC does not. Sitting with the FEH in EV runs the battery down, but it's nothing that a fake shift in low could take care of real fast.

GaryG

[VietVet'67]

Let's clarify.

I'm saying the green graph holds 15 data points for the most recent 15 minutes.
Data that moves off the screen in minutes 16,17,18... is lost. Data is lost when you turn off the key also. (you always get a new "fresh" graph, right? )

I'm saying the white bar... the "Average" number, holds 2000 data points.
Why do I say this? Because this is what was said at the Ford Hybrid "experience" in Dearborn last year

We are on the same page as to the two, really 3, different read-outs - data - is on the NAV screen. Yeah I think, by watching the 15 min graph, it changes at 1 min intervals and is FIFO but I don't think the 'Ave' line is just for the last 15 mins but should be a reading since the last re-set, and the limits of the NAV memory (2,048KB) is what is at fault and not a glitch - probably needs a couple of GIGs of memory to really be accurate.

Another thing I have heard is, when full, the data buffer drops 1000 points at a time to make room for new data.

John – Your computer friend is correct on both the ‘Volatile’ and ‘Non-Volatile’ (Flash Memory). Each byte of computer data is made up of 8 bits of ‘0’s’ and ‘1’s’, so the computer memory (in an 8 bit system at least) is made up of a multiple of 8 (8, 16, 32 . . .. 1,024, 2,048, etc). So it does make sense for what he was calling a page (1,024 bytes) is cleared out and new data takes its place. Just a guess and off the top of my head but this is probably what is happening. The first data point (1 byte) on the ‘New Page’ is/was the last data reading on the average line (which should be an average of all those preceding points) and it starts the process all over again. So yeah – the guys at Ford were probably rounding the number to 2,000.

Now that ‘Throwing out’ a large, and meaningful, chunk of data Would have a Great impact on the Nav MPG average whether it is for 1 tank or if you never hit the re-set and are supposedly getting an overall MPG for say a 2,000 mile trip. That is where the multiple trip setting on the ScanGuage come in handy.

That kind of explains to me why that ‘Average Line’ goes up and down as much as it does. What I am talking about is – I know if I have re-set the NAV at fill-up I can Expect Big swings in the MPG because there is very little data to fall back on. Example: I can fill-up, drive to my house 1 mile away and using EV plus coasting, when I get in my garage the line is at the top and read ‘MAX’. Now for the first few (100 or so miles) I understand still having large swings in MPG – with very small hits of the instant MPG going below the average line. What doesn’t make sense is this same Large swings happening at say 400 miles – if it were a true average that short pedal to the metal would have NO influence on the average because it is so minor – But it does because of the limited amount of stored data it has to work with - - - -!!!!!!

That would also help explain your 110V thing – yeah it was probably using the ICE on time – not the total time you had the key on.

OK guys where is the accurate reading to come from – wherever you have the largest amount of the two set of data needed – Miles and Fuel. I don’t know how much memory the ScanGuage has but probably not enough to be ‘Right’ on the money. The more I think about the system using an average of all the data points it is fixing to throw away makes the most sense.

Hope all this makes sense to everyone else - it doesn't to me

Might swing the money for one of the computer programs that use the OBD data and hook up my laptop to it - got plenty of memory there

I knew this was going to get confusing Gary this is all your fault - making us use our brains like this - I want to be out driving!!

[GaryG]

Hi Phillip

If the Navi 15 min average dropped half the data (1024 bytes) at a time, looks like I would have seen a big sudden change in the average during the last 22,000 miles. This has never happen with my unit. Everything seems to flow as I change my driving conditions.

The SG continued to average new data from the reset at fillup. The Navi average was dropping off data at the same rate it was adding data when it reached it's capacity. Many times I have gone three tanks without a reset of the 15 min average and it always has a smooth change in the average. If a 1,000 (half) data points had been dropped off, my average would have been much more than the 47.9mpg on the 15 min average. The first 200 miles on that tank were with some AC use with my wife in the FEH, and I had to work hard to keep that average at 45.8. I took my gloves off tring to raise that average near the end of that tank. If the last half of the data was dropped, I'm sure the 15 min average would have been in the 50's. My prior tank was in the 50's MPG with no A/C.

Again, we all need to find the capacity in real miles, time and MPG to determine the point which the 15 min average is not reliabe. Up to this point, the 15 min average is within .3 MPG of the SG it seems.

GaryG

[VietVet'67]

Originally Posted by GaryG

Hi Phillip

If the Navi 15 min average dropped half the data (1024 bytes) at a time, looks like I would have seen a big sudden change in the average during the last 22,000 miles. This has never happen with my unit. Everything seems to flow as I change my driving conditions.

The SG continued to average new data from the reset at fill up. The Navi average was dropping off data at the same rate it was adding data when it reached its capacity. Many times I have gone three tanks without a reset of the 15 min average and it always has a smooth change in the average. If a 1,000 (half) data points had been dropped off, my average would have been much more than the 47.9mpg on the 15 min average. The first 200 miles on that tank were with some AC use with my wife in the FEH, and I had to work hard to keep that average at 45.8. I took my gloves off trying to raise that average near the end of that tank. If the last half of the data was dropped, I'm sure the 15 min average would have been in the 50's. My prior tank was in the 50's MPG with no A/C.

Again, we all need to find the capacity in real miles, time and MPG to determine the point which the 15 min average is not reliable. Up to this point, the 15 min average is within .3 MPG of the SG it seems.

GaryG

OK – like John – let’s make sure we are thinking at this the same way, and using our terminologies the same way.
To me we are looking at '3' different data read-outs.
1. A bar that shows instantaneous (Well almost instantaneous) MPG.
2. A graph that shows what MPG we have had in the last 15 mins (probably even these points are averaged over 1 min for each drop or rise).
3. A line that shows the computed averaged since the last re-set – not just for the last 15 mins.

Gary – in my thinking you would be correct in your statement about ‘if half the data points were dropped you would have much higher mpg – that is based on thinking about that average line as Only for the last 15 mins. Like I said in my last post, when/if a total 1,024 points are dropped it would have taken those 1,024 points and averaged them together to get what you would have seen on the screen and started adding new points to that. You wouldn’t really have lost anything.

I am sure that the portion you drove to get the mileage back up was Way beyond the reading when you started, and much bigger than what was being shown on the average line since it is not just the last 15 mins but the total tank. If you had re-set it at that point (but you would have lost the preceding data) it would have been Much higher. Like I said, if the NAV had a second re-set (trip and full tank or beyond) then you probably would have been up in the 50s or even 60s working to get the average back up. I have done it many times myself.

Also we have to take into account – when we re-set the average meter – are we really starting from a cold start, generally not, we have just pulled into the gas station and all is warm and cozy and then we start off with everything hot and a full battery.

I really wish there were three averaged MPG readings. Say on my Acura you have your basic odometers – one for the total on the car, plus, trip 1 and a trip 2 (both of which can be re-set at anytime, I might set one for a single tank and the other for a cross country trip to see just how far we went). If we could have average MPGs on one reading that you cannot change (except say the dealer could re-set when you get delivery – that would be from the very start of the engine till now, and two others. One that you could re-set for say at fill-up for one tank, a trip etc., and the other you could re-set for any other amount – 5mins, 15mins, cold, hot - - - - .

OK – Guys the wife is in the bed and I’ve got to go or I am in REAL trouble.

Later – Plus if someone else has any thing to add or give their option please do so.

[GaryG]

Sorry Phillip,

I view the other two graphs totally useless and am talking about the average white line when I say 15 min average. Moving graphs are the biggest waste IMO.The white line with the average is what I've been talking about all this time.

On a tank average, it does not matter if you start with a fully charged battery or cold engine. It is rare, other than a cold start, I have a fully charged battery. When I pull in for gas, I'm lucky to have a reading on the battery level it's so low. This is my strategy to put energy into and take out of the battery for the best FE using the fake shift in "L" for EV driving.

If the 1,000 data points were averaged before being dropped, than I see your point. I just don't see how that would work. If my son will help us out here, I'll try to get his opinion this weekend. He is a computer science and electrical engineer major at MIT and has driven my FEH many times. He signed up on this site as MattG.

GaryG

[VietVet'67]

To get back to the original question:

Originally Posted by GaryG

How does the SG compare in your vehicle?

GaryG

I can't give you a SG comparison but can give you the difference from Manual MPG and NAVI MPG.


Miles = 5,836.3
Gal = 191.92
Manual Computed MPG = 30.41
18 Tanks - so any inacurate reading should average out.

Average of readings from NAVI = 32.08

Difference = 1.67 MPG

That is a 5.2% difference.

There are just two variables – Fuel used and miles driven. From looking at the instructions for setting up the SG it mentions calibrating the actual miles driven vs the distance shown on the SG. I would think that there is also that same calibration fix for the NAVI also. Both are getting the same data so the difference between the read-out has to be in the calibration of both units – both the accuracy of the distance and the fuel consumption.
I am going to check with my FEH tech at my dealership and see if there is any way of checking/setting these variables to be as accurate as possible.
I am going out today for a medium length trip and will check the mechanical odometer against the expressway mile marker. I will do it over at least a 10 mile stretch. If my calcs are right 10 mile on the road should show up as 9.5 on the odometer - that is saying the NAVI is correct and the odometer is off - We'll see.
Will let you know the results later.

Did you get with your Son this weekend to see what he thought about the whole thing and as to how he might think the two units are coming up with results??

UPDATE: I did go out today and checked the odometer but not for as long of a length as I had wanted to but will work to get a more accurate reading. What I did ovserve was over just a 3 mile stretch, the reading was a minus 1/10 of a mile (close as I could get at the short distance). So I would have been going faster than the speedometer was reading and have gone a longer distance than has been indicated. If you take that actual 3 mile and use the 3.1 reading to convert that reading to get MPG then the NAV system reading is the more correct one. Guess even though it is digital the tweeking is off - for the good - 10K actual miles would be around 9,677 reading on the odometer. Will check on a much longer trip to get a more accurate conversion factor.
Using this crude data, plus what I had observed about the speedometer reading 45MPH and a radar gun showing I was going 47MPH. it gives me a factor of 1.04 and using that number to multiply by my computed MPG is VERY close to the NAV reading.
So I would say the NAV and SG are very close in overall tank or trip.