MPG clock start with the same figure that it ends the day before.!!?

[guest1381]

Hey up.

basically as the question asks.   
 
when we first bought the car 6 weeks ago I'm sure the  mpg clock was saying 30ish mpg when the car was started for the first time in the morning (cold).  This would gradually go up as you drove about. 

but now when i start the car in the mornings the car is reading the same as when i finished driving the day before.

Also how fast is this clock supposed to fluctuate when driving?  It could say 55mpg on a motorway then when i come off the motorway onto minor roads the clock isn't coming down fast to enough to indicate a true reading of mpg driving at 30 mph...

thanks for any help

[DV]

I`ve exactly the same thing.

When you reset the mpg counter when you filled up your car, the counter starts calculating and showing the average mpg of the car. (In my car about every 10 seconds updating the value).
The mpg counter shows you the average always. If you drive in the town shows you 30mpg-ish, on the motorway it counts up 50mpg-ish, come back to city it goes down. When you go to fill up again you will see the sum mpg (I guess 40 mpg-ish).
If you want to see separate the mpgs, reset the counter before you go on the motorway, and reset again when you are back to the city. In this case the computer won`t save each value, just the last one.

I hope it helped.

[guest1381]

i didn't understand what you meant.   I didn't think you could reset the mpg clock??? i know you can reset the trip clock but not how many mpg you are doing.


Ive just been out to car and started it and it says 53mpg what it said yesterday after i left the car last night.   Now when i drive away now its saying I'm doing 53mpg which obviously is not true reading.

could this be a wiring fault which is causing the mpg clock not to show correct reading??

thanks

[guest1328]

You cannot reset the MPG display itself.
It is only a rough estimate of fuel used set against the mileage on your trip reading.

Hence - overnight - you haven't moved, so the trip & mpg read the same. 
Reset the trip the MPG computer starts again.  After the reset you will see its display change rapidly as it has no data to work on.

Its only a rough guide.

[chrisv]

Hi,
Press the button until you have the trip setting, hold the button in which zero's the trip reading and your mpg reading will also be zero'd, alternatively don't worry about it, it's only a rough guide
Chris

[culzean]

If you really want the most accurate 'mpg' figures I would zero the trip mileage every time you fill up with fuel, otherwise the previous mileage and fuel usage kinda muddies the equation. You may notice that after the 'trip' is reset the 'mpg' display reacts very quickly to (for example) going up and down hills, but as the trip mileage rises the sensitivity of readout decreases, this can only be because the computer is taking all previous fuel and mileage into its calcualtions and giving an average spread over a much longer period.

Depending on driving style I have seen about a 10% error on Jazz mpg readout vs real life fuel used.  Agressive driving delivers the worst error, steady driving the lowest error. (display only updates every 10 seconds and takes a 'snapshot' of the rate fuel is being used at that time - so if driving is erratic it will sometimes miss some of the peaks during rapid acceleration).

Air temperature seems to affect mpg a lot, I drive 50 to 60 miles each day and get much better fuel consumption in the summer (high 50's mpg) than in winter (high 40's mpg).

[guest1408]

mine shows 46mpg while idling in a traffic jam    I personally think that this computer read out is a waste of space and electronics since it doesnt give you any accurate picture by which to adjust your driving dynamically.  I now use an iphone app in which I record my mileage, quantity of fuel and cost at each fill up which gives me an average reading over a period - that is the only useful thing to know as far as I can see. (its called Road Trip Lite - free app)

On another issue I notice that when I fill right up I can do as much as 100 miles before their is any visible change in the petrol gague - maybe another "Honda feature" to try and convince us how economic their cards are 

[nowster]

On another issue I notice that when I fill right up I can do as much as 100 miles before their is any visible change in the petrol gague - maybe another "Honda feature" to try and convince us how economic their cards are 

Not another Honda feature. I had a Micra that did that too. It also took a while to notice any small top-ups. The gauge can only measure what's in the tank. When you fill to the brim, you're also filling the pipe from the filler cap to the tank, which the gauge cannot measure.

[culzean]

The mpg readout will always start again a the last figure in its memory (ie when you turned the engine off last time), as far as I know this will be the same on any car.

Every car I have ever had has stayed on full for a while after tank has been topped up till the petrol pump cut out, because you have filled the filler pipe to the tank as well, and on the Jazz this goes from filler cap to under the drivers seat, quite a length of pipe!

If you want a truly 'dynamic' readout from the mpg reading I suggest you zero the 'trip mileage' display every time you fill the tank, this will also zero the 'mpg' readout.  The mpg reading will now react very quickly to changes in your driving and gradients in the road etc.  The more miles you have accumulated on the trip mileage the slower the mpg readout is to react, as the mpg is knid of averaged out over the whole of the figure on the trip mileage.  If you stop in traffic the figure on the mpg display will gradually drop as you are using petrol but not going anywhere.

The mpg display is updated about every 10 seconds, and the smoother your driving the neared to actual mpg the readout will be (every time you use the brakes you are wasting fuel, and the harder you brake the more fuel you just wasted).

Remember that in warmer weather your car will use less fuel than in cold weather, so don't be surprised if you get 10 to 15% better mpg in summer than in winter in like-for-like driving.