Distance to Empty fluctuates excessively

[Rick60]

I realize the 'Distance to Empty' display is just an approximation based on previous speed/fuel consumption/driving style and will vary from city to highway use, but my display will vary more than 100km from one to the other or even ~50km town driving only. Let me give an example of what happened this morning...

Firstly you should know i live in a country town so my speed can vary from 50km/h to 100km/h within a short distance.
I left home with exactly 1/4 tank of fuel (63L tank) and the Distance to Empty reading 120km, after idling along the dirt road until it warmed up and reached bitumen, i then travelled at 80km/h for a short stretch and the Distance to Empty read 70km (ok, the engine was cold). 50km/h for about 5km through the town before i reached 80 then 100km/h zone. Somewhere along this 100km/h stretch the Distance to Empty had risen to 180km then i got to the next town (25kms away) with a similar 80km/h buffer zone and 60km/h limit. Driving through this town the Distance to Empty got up to 220km (weird!).
Then i made the return trip, when i got back to my home town the Distance to Empty read 150km and the fuel gauge was just under 1/4 (about a needle and 1/2 thickness), i decided to fill the tank up. It took 52 Litres of fuel, and the Distance to Empty reset itself to 570km, but i'd more likely get well over 600kms to the tank full.
My driving style is such that i don't accelerate or brake quickly unless i need to, when climbing a hill i'll let the speed drop slightly before easing on the accelerator to keep a steady speed or catch up without making the transmission kick-back unnecessarily, and i'll let the car slow itself down before braking for a corner. You might think i drive like an old fart but i'm not that bad, i'm just sensible, not a hoon.

Does anybody know what would cause the 'Distance to Empty' to display so erratically? I'd really like to fix or at least understand what's going on because i'd like to be able to 'trust' what the display shows, well... as much as this kind of display can be trusted

 

[Woody_SS]

Can be as simple as the car is on a hill. With such a low amount of fuel it will only need to be slight


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[sexyvz]

Mines the same sorta. Could have quarter of a tank park on a hill or in a park with a slight slope to the side start it up and it reckons it's empty but the. Slowly sorts itself out. Think the fuel reader thing in the fuel tank might be bent or dodgy. My mechanic told me there's an arm in the tank and if it bends while bein made or if the tank has been worked on and the metal arm has bent while bein put back together then it's gunna throw ya fuel reading out.

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[Immortality]

It is fairly typical, distance to empty is calculated over distance/time and is an average. You'll find as the tank gets low the distance to empty will come down fairly quickly. Cruising @ 80-100km/h is much more fuel efficient than stop/start driving @ 50km/h.

Right now mine is showing 65km to empty but the low fuel warning hasn't gone off yet but I know the tank is getting low and I've been doing a fair amount of around town type driving. Once the alarm goes off I know there is about 7 litres left and distance to empty will be fairly accurate.

You can also double check that the calibration numbers for the trip computer are correct. With the ignition in the on position hold down the and 'SET' button. After a few seconds the display panels will change. It will then either show FUEL with a number or DIST with a number or Tank with a number. Both the FUEL and DIST should be set to 625 and TANK 0.0 as the default settings. To change between the three you need to let go of the 'SET' button, use the 'MODE' button to change to the next screen and then press and hold 'SET' button again. If you want to change one of the settings, once the setting comes up, use the up or down button to adjust.

edit: all of this info is in the owners manual

 

[Grassie]

could be the fuel sender wearing out... is it playing up with more than 1/2 tank?

 

[VR38]

Does anybody know what would cause the 'Distance to Empty' to display so erratically? I'd really like to fix or at least understand what's going on because i'd like to be able to 'trust' what the display shows, well... as much as this kind of display can be trusted

Sounds like distance to empty is working normal to me, it's a calculation of how much fuel the car is using at the speed you are travelling and a reflection of how much fuel is left in the tank.
Eg;
Full tank/hi way driving, high distance to empty reading.

stop start driving/empty tank, low distance to empty reading

and everything in between

 

[VR38]

My driving style is such that i don't accelerate or brake quickly unless i need to, when climbing a hill i'll let the speed drop slightly before easing on the accelerator to keep a steady speed or catch up without making the transmission kick-back unnecessarily...

If you have distance to empty display you must have cruise control, if you are a fuel miser then using the cruise control is a must, there is no way you can compete with the computer with minute throttle openings etc.

 

[Rick60]

Woody_SS:
No, it's nothing as simple as parking on a hill, or lean. My garage & drive are level and the roads are mostly level except for some minor hills in the area.

sexyvz & Grassie:
It's had no work done on the tank or the float/sender, it 'looks' to be original or not touched in quite a while. I don't know how long it's been doing this, i've only had this car for a few months and i'm trying to fix up all the annoying bugs. It doesn't matter how much fuel is in the tank, the Distance to Empty will fluctuate over 100kms on average (much more with a full tank). I can accept fluctuations due to hilly<->flat roads or town<->highway driving, the fuel usage varies from 7-11L/100km for average roads climbing to 20L/100km going up hills but will drop back to about 4 going down. town driving is not much different although has more slowing-down & speeding-up.

immortality:
What you mentioned is what may be the problem although i've already searched a lot regarding the calibrations without any definitive answers. What i have found is that two of the modes (i have to press & hold 'Set' to get these) should display 625 and the other should be 0.0.
It seems different vehicle models need different combinations of button-press to get diagnostic/calibration displays, mine is press & hold 'Set' while switching 'On' the ignition to get the digital speed readout in the left display, then pressing 'Mode' a couple of times for the LCD diagnostic display. To show the calibration displays, i press 'Mode' to cycle the three while the ignition is 'On', then press & hold 'Set' in each mode.
Here is where i don't know what to do except to make sure they are at the defaults mentioned above. The calibration instructions are not included in the VS owners manual!
I'm not sure which is which but one mode shows in the right display '625 cal', the next mode shows in the centre display '625cal', and the third (fuel?) mode shows in the centre display '61.3L Tank' and in the right display '.0cal' (the tank is 4km from full so 61 is close enough).

OK, so these calibrations should be ok i think, one of the 625 cal ones is speed/distance adjustment for non-standard tyre size/diameter, kms traveled and speed seem to be accurate. The .0cal one is for fine-tuning the low-fuel warning and also affects distance to empty but as it is currently showing 61L for my 'full' (63L)tank, i guess that means there's a 2L+ safety margin for the low-fuel warning. The last 625 cal ? i have no idea!

This is why i can't understand why there is wild fluctuations in the 'Distance to Empty'. There must be something else causing this and i hope someone has an idea.
Now this is just wild speculation but would it have anything to do with fuel flow? could that affect how the computer calculates fuel consumption and distance to empty?
I've read in this forum something about fuel flow but understood none of it.

Sorry this is so long, i want explain what i have so someone can suggest something that i may have missed. - Thanks for the suggestions so far

VR38:
70km to 220km variation for 1/4 tank of fuel - highest (220km) driving at 60Km/h - something's wrong here!
and...
You're right, i do have cruise control and i do use it, but not on winding single-lane roads where there's traffic ahead or hill climbing and it unnecessarily kicks-back just as i reach the top of a hill. Not concerned on the freeway though, just hit auto-pilot and swerve around the moving road-blocks.

 

[Jxfwsf]

625 is default, not 125.

Destructions:


A slight hill while driving will not change the dte instantly, there is a time limit before the trip computer changes the readout to avoid this sort of thing, same as when you only put $10 of fuel in, it doesn't work it out for a few minutes, needs to be a change of around 24 liters i've found before it instantly recalibrates the dte.

You have it right and as suggested it's fairly normal for a drastic change to occur between highway/freeway driving and town driving, I get much the same fluctuations on my daily drive to work, lots of km's left when on the highway, about half of that when i'm in the 40-60 zones, it's accurate... for the conditions at the time.

 

[Rick60]

625 is default, not 125.

A slight hill while driving will not change the dte instantly, there is a time limit before the trip computer changes the readout to avoid this sort of thing, same as when you only put $10 of fuel in, it doesn't work it out for a few minutes, needs to be a change of around 24 liters i've found before it instantly recalibrates the dte.

You have it right and as suggested it's fairly normal for a drastic change to occur between highway/freeway driving and town driving, I get much the same fluctuations on my daily drive to work, lots of km's left when on the highway, about half of that when i'm in the 40-60 zones, it's accurate... for the conditions at the time.

Thanks for the Destructions I'll put them to good use and check the fuel flow calibration. It's going to take me a while to go through 5 tanks of fuel but hopefully i'll find something wrong and this is what's messing up the distance to empty. It makes sense, if the fuel flow calibration is out then it's miscalculating the amount of fuel being used and the distance i'd get from that miscalculated fuel consumption.

I'm aware of the lag as it averages out the fuel used to distance traveled, that's acceptable. It's just that the change seems too drastic, especially when i can estimate myself how many kms i should be able to get if i'm using 10L/100km or 15L/100km, the Distance to Empty is just too unreliably erratic, i would be just as well off guestimating the old-fashioned way from the fuel gauge.