trip computer erronous fuel reading

[Immortality]

My trip computer is showing a higher fuel usage then is actually being used. if i reset the trip computer when i fill the car, then drive it till empty and fill the car again it shows i've used some 68ltrs however the tank only holds 59 ltrs and a normal fill is about 53ltrs so it's saying i'm using some 15ltrs more than actual usage or a 22% variation:bang:
how does the trip computer actually calculate the fuel usage??

 

[Fekason]

Trip Computer Calibration?

Hi,

Is it cloudy over there today?

The most likely possibility is that the fuel flow calibration number has been incorrectly set. Check that it is set to the default 625 or thereabouts. If not, set to 625 and go through the calibration process.

The calibration process allows + or - 25% or so, for both fuel flow and distance adjustments. Distance affects the trip meter readings, but not the odometer. Thus errors of the magnitude that you report are possible from incorrect calibration.

 

[Immortality]

Hi,

Is it cloudy over there today?

The most likely possibility is that the fuel flow calibration number has been incorrectly set. Check that it is set to the default 625 or thereabouts. If not, set to 625 and go through the calibration process.

The calibration process allows + or - 25% or so, for both fuel flow and distance adjustments. Distance affects the trip meter readings, but not the odometer. Thus errors of the magnitude that you report are possible from incorrect calibration.

Ok got you on that one, you hold a couple of the buttons when turning on the ignition, if i remeber correctly i've done this and they were at the lowest number they will go (500 i think) i've never actually checked the trip km to the odo so i mighthave to do that as well.

what is the actual "calibration" process

as for the weather, it's a perfectly clear sky over here, but thanks for asking:thumbsup:

 

[Fekason]

Try default settings.

I would set the following settings:

Distance 625
Fuel flow 625
Fuel Quantity 0.0

That should work out very close.

If you are pedantic like me, you can check the trip meter over a known distance (say between 5 km posts) and apply a correction. If the trip meter is less than 100 km, then it reads to 10 metres, which allows good accuracy.

With new tyres, I find 625 perfect, changing to 631 as tyres near their legal wear limt.

With the fuel flow, record the trip computer quantities over about 500 litres and compare with the actual fuel added. Best if the first and last fills are at the same pump. My fuel flow is currently set to 646.

I have a copy of the instructions some where, so PM me if you would like me to e-mail them to you.

Cheers.

 

[shaggerz]

Has it been doing this since you got it?

There is a switch on the bottom of the instrument cluster that selects what size fuel tank you have. This may be set incorrectly if the instrument cluster has been replaced. I imagine there is a small chance this may have something to do with it.

 

[Fekason]

Calibration Instructions.

For those interested, calibration instructions for VR/VS trip computers are attached.

 

[Immortality]

it's always been like this, however i had discovered the calibration numbers earlier but didn't know what they were suppose to read and when i got the vehicle both were on 500 which is now obviously way to low. i've never had the cluster out so i don't know about that switch and it doesn't look like it's been touched(cluster that is). i was under the car yesterday looking into a suspected driveline vibration, anyway i noticed that the return fuel line has been damaged at some stage and is partially crimped/kinked(like when you bend a fuel line in half), not totally but there would definitly be a flow restriction there. could this effect the fuel usage reading?? think i might get a pressure gauge and test the fuel pressure as well, maybe this is also causing excess fuel usage?? does anybody know what the fuel pressure should read??

cheers