Consumption - computer data input

Honest John Back Room » Motoring discussion
View Threaded
Tue 9 Sep 2008 12:56
Consumption - computer data input - Andrew-T
In-car comsumption calculations have been discussed recently. Can an expert (or several) explain what inputs the computer uses? Is it more than counting the number of injections to the manifold and assuming a volume for each, plus counting roadwheel revolutions and assuming a rolling diameter/circumference?

And 'distance remaining': the system clearly doesn't know how much fuel the driver puts in, so the tank sensor is used; but this is notoriously vague.
Reply | Report as offensive | Link
Tue 9 Sep 2008 13:18
Consumption - computer data input - Peter D
Systems vary but the computation uses the injector pulse width, road speed, engine RPM and distance travelled And yes it does use the fuel gauge when you fill up and averages the reading for a few seconds when it detects a significant change in fill level. Mine appears suprisingly accurate, Audi A6 1.8T. Regards Peter
Reply | Report as offensive | Link
Tue 9 Sep 2008 13:23
Consumption - computer data input - Andrew-T
So 'distance remaining' is counted down from the moment fuel is added to the tank? I can see scope for a cumulative error here? SWMBO's Clio used to suggest ridiculous possibilities sometimes.
Reply | Report as offensive | Link
Tue 9 Sep 2008 13:49
Consumption - computer data input - Altea Ego
It matters not really what inputs they use. The data displayed should not be relied upon, and is for comparative purposes only.

For real MPG use brim to brim methods, and for knowing when to fill up use the guage or warning light,


Reply | Report as offensive | Link