On board computer question

[davie24]

Hi folks.
Being a new owner of an 07 Vectra sri,I have a query about the on board computer and the info it shows.

For some reason which is beyond me,when viewing the mpg, the display has a habit of showing 999.99 mpg.This does not happen all the time,but seems weird.

Any advice would be welcome before I take the car back to the dealer I bought it from last week.

Thanks
Davie

[6009tristanb]

its when you are driving and you let off the accelerator i think its because its using no fuel to move you along whilst your foot is off the accelerator if you keep it in the same gear when your slowing down to stop instead of dropping down a gear to slow down you will notice it stays at 999.99 mpg untill you put the clutch in which means all that distance you were slowing down you didnt use any petrol
they might be a proper saying about it but this is my interpetation

[john_k_sri]

It is 'run-on' when you lift off the accelerator at any speed, and very little fuel is used until the ECU calculates that more fuel needs to be injected, as momentum is lost. The higher the speed/rate of momentum the longer the 'runon' lasts. I assume it is the same for both petrol and diesel engines.

Yes, it's weird. It is much more noticeable on the facelift, due to the much larger and more-prominent central display of current mpg.

[john506]

Mine does it sometimes when I coast

[davie24]

Thanks guys for your input.I tried coasting on the way home from work earlier,and it did exactly as you said it would while the engine was not under load.

Many Thanks
Davie

[hebblemarine]

If you set it to European units, it will show consumption in L/100km, it will show 0.0L/100km. Fuelling is shut off on the over-run, but as our units are the 'other way round, this would cause a 'divide by zero' error: something divided by nothing. It's just a software coding tweak: you're not really doing 999mpg, you're doing an infinite number of miles/gallon as no gallons are being used

[Robsey]

Yep as described - whenever the engine is on "over-run" - that is braking, decelerating or coasting, as this is when the injectors are turned off, and so not delivering fuel.
Hence you are doing an infinate number of miles to the gallon.
999.9 is the nearest value to infinity that the fuel computer can display.

It will drop to a much lower value if you dip the clutch, or touch the accelerator pedal.

It will do it on ALL Vauxhalls with a fuel / trip or board computer... even my 1994 Cavalier. Both petrol and diesels