Fuel consumption display lying?

[Dr_No]

Do people find the fuel consumption display with the odometer/trip computer thing is accurate?

I normally get around 4.9 to 5.2 l/100km from my tanks on the display but the last few tanks, I looked at how much actual fuel it took to fill it up and how many km I had done and it worked out around 5.6 to 5.8l/100km which was around 0.7 more than the computer displayed.

Has anyone else noticed this?

[aaronng]

It's always like that. Fuel computer is too optimistic.

[vividjazz]

Mines the opposite. I get better economy is reality than the display.

[Pogi]

Different quality of fuels that you pump?

Computers can be a bit fussy.

[m3ntAL_l2]

yea, my alert thing beeps when goin up hill and then stops when im goin down hill :(

[08ESE]

mine changes its mood all the time

[Pogi]

Alert thing? :confused:

[08ESE]

his avatar is a commodore, so id say its an ecu error :p

[preludacris]

LOOOOLLl @ O8ESE

funny coz its prolly true

i think what he means by alert thing is the low petrol light ?

if so .. its just coz ur petrol is swishing around in the tank man.... lolz. NOT coz ur car is possesed or anything .. :D

[civiceg9]

his avatar is a commodore, so id say its an ecu error :p

lol :D

You can only get an estimated reading from the tripmeter.
If you dont reset it after each refuel, it will avg out the old readings.
I have the worst reading right now. 9.7/100km from my Jazz.

[TypeR_DC5]

the more I reset, the higher rating I get~~:(~~

[revolution]

Not sure about you huys, but I get like average 8.2L/km on my '05 VTi-S. Been like this since day 1 of picking up the car from the dealer. Will it improve as I put more K's on? It currently has 9500km's on it.

[AmateurJazz]

Alright guys, this is what you do for an accurate reading:

When you fill up at the pump, record down how many litres you had filled up. Then go to your trip computer and record how many kms you have travelled since you last filled up.

Divide the total kms by how many litres you have put into the car, this will be how many kms your car uses per litre.

Divide this result into 100. This is your fuel consumption per 100kms.

Using my last figures as an example:

1) I filled up at the pump, recording 37.8 litres.
2) I had got 585.4kms from the last fill up.
3) 585.4/37.8 = 15.49kms per litre
4) 100/15.49 = 6.455L per 100kms

If you want to be even more accurate repeat this process for about 10 fill ups and average out the result. My fuel consumption ranges from about 6.4 - 6.9L per 100km, which shows my trip computer is quite accurate as it is almost 6.8L every time I go to fill up.

[Pogi]

the more I reset, the higher rating I get~~:(~~
That's normal. After I reset mine, I thrash it and bag. 17.1L/100km.

[Poeter]

Mine gives low rating if i drive conservatively for the first 150km and after that the computer doesn't fluctuate as much even if i start driving aggressively.

However, it displays high ratings if i drive agressively right after a reset the computer and will remain rather high even if start taking it easy on the accelerator.

[mIKKYbEEZ]

Here is the problem. We live in Australia. That is a good thing in many cases, but not when it comes to getting anything done from Honda Australia. I saw that in the US there was a Honda FIT TSB (technical service bulletin) mentioned here :

http://www.fitfreak.net/forums/2nd-generation-ge-08-present/51226-tsb-software-update-inaccurate-mpg-display.html

The actual bulletin is here:

http://www.scribd.com/doc/22910166/Fit-MPG

What it is basically saying is that the software used to calculate the mileage (mpg) is too optimistic and reports HIGHER miles per gallon than actual.
There is a fix for this (in the USA) and it works perfectly.

For us in Oz, we use the Litres per 100kms and I think (but I have no real proof) that the same software is used on MY09 Jazz VTi models (at least that is my vehicle). The difference in the US and here (OZ) is that the software uses different conversions factors and constants (eg US Gallons vs Litres, Miles vs Kilometres and whatever other ancient measurements the US is stubborly hanging on to).

I spoke to a "NSW technical specialist" last year about the ridiculousness of the display showing LESS L/100kms than it actually does (I can do my own calcs to find out the real fuel economy). the so called expert was a total idiot and unbeknownst to him and his offsider I recorded the whole insane conversation. They would not agree even to look into what I was saying. I know why, it would cost Honda Australia money to do the reflash of the ECU with the firmware and software.

I hope this has been helpful - if enough people print out the TSB from the US and show it to their dealer or service centre, then Honda will get the picture instead of fobbing off sheeple in the way they are used to.

I am an engineer who loves things to be perpendicular and parallel - The attitude of "She'll be right" just doesnt cut it with me.

I really enjoy driving the Honda Jazz, I think it is a beautiful vehicle. The fuel economy gauge is disappointing.

Here are the relevant points from the TSB - remember US MPG is inverse to Litres per 100 km ....so where it says "higher" read "lower" if you are in Oz

SYMPTOM The information display shows the fuel mileage to be
10 to 15 percent higher than the customer’s actual
calculated mileage.
NOTE: Verify that the customer has correctly
calculated the mileage by dividing the miles driven by
the number of gallons used.
PROBABLE CAUSE The PGM-FI software bases its fuel calculations on an incorrect data set. CORRECTIVE ACTION Update the PGM-FI software with the HDS. NOTE: The update does not address complaints of
poor fuel economy, and the customer should not
expect an improvement in fuel mileage. This update
only allows the information display to match the
customer’s calculations more accurately.

[Artie]

From brand new, when refueling I have always trickle filled my tank right to the top. I've never put less than a full tank in. I have always reset the trip metre/fuel usage indicater at each fill up. I have recorded all data from each fill up every time including the l/100km number displayed in the dash. At the last fill (at 46,492km) I had done 99 fillups so there is heaps of data there for me to use.

By calculating the actual amount of fuel used according to the car I've found that on average it is extremely accurate.

For example if the indicater says I've used 6.0 l/100 and I fill up after doing exactly 500.0km it is saying that I've used 30 litres.(6 X 5 = 30)

So, in my real life experience, by doing this calculation on all of my 99 fill ups, the car's computer is telling me that I have used 2933.00 litres. The total of actual litres used according to the fuel bowsers is 2953.27. That's pretty bloody close in my opinion and any error could also be in the accuracy of the fuel bowsers as well.

[sdx91]

yeh its inaccurate for me too.. very annoying :(

[mIKKYbEEZ]

You (Artie) are so lucky to get some very accurate readings, I have heard from a family member that their '04 Jazz has spot on fuel economy readings on the display. From what I have read in forums elsewhere the inaccuracy is pretty much isolated to the '09 model of Jazz (and Fit overseas). The TSB i have posted applies to a specific year of Honda Fit and I think we in Oz are also not getting the right readings for the '09 models. I have done readings over roughly 6000 kms to ascertain the inaccuracy and every time the readings are between 10 to 15 % incorrect (with the display being too optimistic giving lower values than actually calcualted ones). It would be interesting to know what other people get for their fuel economy. Please do specify what year and what model and what transmission you are running (MT or AT). At the last tank for example, my low fuel light came on at 550km (meaning that there is 42 minus 7.9 = 34.1 litres left in the tank - and I filled it to the neck as I always do). The fuel economy on the display was 5.3 l/100km. Calculate the TRUE fuel economy and it is 6.2 L/100km. Clap clap clap Honda :) 17 percent difference and its always in this range (of inaccuracy). I have emailed the "service" centre in the upper North Shore in Sydney asking them if there has been an update for the software and so far I just hear crickets in the background...........

[Artie]

Mine is an '07 GD 1.5 VTI-S, manual gearbox. My experience is not that every tankful is accurate. Sometimes my consumption reads over and sometimes it's under. More than half the time my indicator reads within 5% of the actual. The design of the fuel tank is such that it is easy for air locks to restrict the amount fuel that the tank will accept. This can differ on each fill up depending how fast the fuel is entering the tank, how full the tank already was and any ground slope that may exist. This can lead owners to mistakenly suspect that the trip computer is inaccurate.

My fuel consumption display tends to be more optimistic with constant speed highway driving. It is usually more pesimistic when using E10 (I rarely use it though because my actual consumption increases by around 10%).

Overall though, it is great to use as a guide but shouldn't be completely relied upon.

I know how well I'm going by the fuel guage. I like to get to more than 300km before the guage reaches the half full mark.