recalibrating fuel economy reading

[vskclint]

Hi guys,

Has anyone had any luck with recalibrating the fuel economy in their trip computers? I have a 2012 d40 and it show at least an extra 2 litres per 100 being used. It was recently checked using the old method of km's driven v's litres to fill

 

[Old.Tony]

I've never found them completely accurate. My Navara doesn't show it although the ECU has the usage data, the instrument cluster doesn't keep track of it.

I keep track of it with the Torque app but even this app is easily manipulated and not accurate. We have another car here that consistently reads around 2LPHK below actual consumption, so you might think you're doing well, but when you refill and calculate you get disappointed ...

I think they're not much more than a useful guide. I'd prefer them to calculate actual fuel used over distance since last fill, but they seem to work on an average-over-time of current LPK rate.

In our other car, the display auto-resets after it detects the tank has been refilled. I don't know if the 2012 Navara does anything like that - do you refill when nearly empty or just whenever you see a good deal on fuel?

 

[landmannnn]

First things first... Your odometer reading is incorrect, measure it against a known distance and you will see it overheads by about 8%.

Secondly, fuel consumption is very difficult to measure. The normal method is to use the time the injectors are open for and guess the amount of fuel that flowed through. There are many variables that will make this inaccurate (temperature, injector condition etc)

Some vehicle manufacturers in-house software (VAGCOM for example) allow recalibration, I don't believe Nissan Consult has this functionality.

 

[paddyjacka]

First things first... Your odometer reading is incorrect, measure it against a known distance and you will see it overheads by about 8%.

Secondly, fuel consumption is very difficult to measure. The normal method is to use the time the injectors are open for and guess the amount of fuel that flowed through. There are many variables that will make this inaccurate (temperature, injector condition etc)

Some vehicle manufacturers in-house software (VAGCOM for example) allow recalibration, I don't believe Nissan Consult has this functionality.

I agree the odometer on my 2013 d40 is out quite a bit. Using the Waze app when I reach 100 kms/hr the odometer says 108 when on cruise control and 117 when I am actually doing 110 kms

 

[Old.Tony]

We have 3 cars here and 1 motorcycle.

The motorcycle's speedo (needle-on-spring, mechanical drive from front wheel) is fairly accurate (it displays about 1km/h above the actual speed measured by radar or GPS). Odometer is mechanically linked to the cable.

The Hyundai reads very similar to the bike, although like the Navara it gets speed data from the ABS sensors and electrically drives a needle-on-spring speedometer. The odometer is a calculated figure from the number of rotations of the wheel (factory standard wheels provide a specific distance for one rotation allowing calculation of both distance and speed).

My Navara gets its wheel rotation data from the ABS system like the Hyundai but is woeful in speed indication. When queried, the ECU actually has a fairly accurate idea of the speed and distance (I have standard size tyres on) and thus the odometer is quite accurate but the electronic needle-on-spring is dismal and is somewhere around 10km/h out at 100km/h.

The final vehicle is a Mitsubishi with a full digital display (its entire dash is a TFT computer screen) and all of the information is identical to the ECU-computed information (I have checked by querying the ECU). Speed is indicated in an analog-fashion with a graphically-displayed needle (no physical spring deflection like the other vehicles) as well as digitally on the dash and the HUD.

So while my Navara knows the actual distance and speed rather well, its display of the speed is rather poor. Nissan themselves won't do anything about it because as far as they're concerned, it's compliant with Australian Design Rules which state that the speedo:

* Must not display a speed less than the actual speed at any time
* May display up to 4km/h plus 10% of actual speed OVER the actual speed, so at an actual speed of 100km/h, the speedo is allowed to display up to 114km/h

Anything within that range is compliant and therefore there's no need to adjust it.

Changing the displayed speed by changing the tyres actually makes the Navara inaccurate (I've tried this as well).

If you want to see how your car is doing, get a device to query the ECU in real time. On standard tyres you'll find that your distance and speed are actually quite accurate, the ONLY thing that's not accurate is that ruddy needle in the dash.

Quick, cheap and simple solution: use a GPS for speed indication.

 

[Bruce Brodie]

I agree the odometer on my 2013 d40 is out quite a bit. Using the Waze app when I reach 100 kms/hr the odometer says 108 when on cruise control and 117 when I am actually doing 110 kms

I had a similar problem, turns out by changing your sidewall size from 255 65 to 265 X 70 will give you about 3 ks difference the 70 is 70 % the with of the tyre = the height, a good tyre fitter can explain it better, mines a 17'rim as it's a 550 and I also use Waze at 103 Waze is registering 100., Same 3 K difference at 80 and 110.

 

[Erick]

Big difference in rolling diameter. 11-12percent. So at approx 92 kph on new tyre will be 100 Kph on old.

 

[Bruce Brodie]

Sorry should have made that clearer, the standard size on a D40 STX 550 is 255 X 55 x 17 I upgraded to 265 X 65 X 17, that brought the accuracy of the GPS to within 3 klm of the speed limit i.e. at 83 klm by the speedometer I'm doing 80 by the GPS same 3 klm difference at 100 and 110.

 

[Bruce Brodie]

Big difference in rolling diameter. 11-12percent. So at approx 92 kph on new tyre will be 100 Kph on old.

As I said it's best to talk to a tyre fitter about it as he can explain it better, also at 2000 rpm she is doing 115 klmh by the GPS, much lower revving than the 2.5 ltr 4 cyl.