Accuracy Of Trip Computer Readouts

[cro142]

The trip computer on my BAII Turbo ute seems to give a wildly incorrect readout of average fuel consumption. I had suspected this for a while, and last week did a test which confirmed it.

Over a full tank of fuel (~70 litres), and with the AVG L/100 zeroed at the fill, the trip computer read an average of 16.5 L/100km.

However, using the old manual method of calculating the consumption from litres used and km travelled (neck to neck fill at start & finish), I calculated a consumption of 13.3 L/100km.

Having used this manual method for calculating fuel consumption for many years prior to trip computers, I am satisfied that I can do this accurately.

So, why the huge difference?? - 16.5 by the trip computer, and 13.3 by calculation!!

Any ideas ??

[Iconic Bionic]

Gremlins.

well mine has only travelled 74K's (not 74,000) so I'll be keeping an eye on it.

[stang]

Gremlins.

well mine has only travelled 74K's (not 74,000) so I'll be keeping an eye on it.

There is no accuracy treat as a guide only.

[Cashie]

In all three of my BAs it has always read about 1l/100kms higher than when I manually work it out..

[bad inferno]

don't really know however have come to this conclusion:

In the old days they could just measure the flow into the carbie with a simple flow meter, very accurate. However now with fuel injection and a pressurised header and return line you cannot measure the fuel supply anymore. I think they just use an estimate based upon injector frequency.

rob

[BlueXR6Turbo]

Not long after I first got my car I compared the trip computer with manually calculated fuel economy, and it worked out to about 2L/100km difference. So it seems like they're all out a bit. I think the trip computer is really only any good to compare your fuel economy with how it has been historically, e.g. if it's getting better/worse.

[cro142]

Yeah, it seems these readouts are consistently off.

I have had 3 other BA's and the readout was off by about 1L/100km - but this one is off the planet with a difference of around 3L/100km.

Sure makes for a depressing read before you know not to believe it!!

[Paradoxx]

They aren't the most accurate way of measuring how much fuel you use, nor is your actual fuel gauge accurate enough to swear by. Even the speedo has a few km/h difference in EVERY falcon. All these little discrepencies will lead to a larger error with averages. Also if you have a look at the trip computer vs your odometer, you will notice the 0.1 will stay on the trip but the odometer will start from 0.0 every time you turn on the car. So effectively you could travel 0.9km and turn off the car and the odometer will reset to .0 again, and to tick it over you would have to drive a whole km for it to do so.

I think I just confused myself.

[XtRmn8]

My trip computer is not 100% accurate on consumption nor the DTE.

For example my average consumption per 100km is about 0.5l more then what it is when I work it out manually. Also the DTE is not very accurate at all because the tank in a sedan is 68l and I have had the DTE down to 20km and I could only fill 60l max and that is will fuel spiling over the floor!

[gogo]

My understanding is that the trip computer works off injector duty cycle to calculate fuel usage. This is why it is off the planet if you have bigger injectors and a piggy back ECU.

I have typically found mine is out by approx 5% (higher fuel consumption on computer than actual fuel consumption) over obout 80,000kms.

Really not too bad an indication. 3L/100km seems very large error. Average this out over 5 - 10 tankfuls and see if the error stays as large...

cheers,

Ben.