Trip Computer

[tonycommander]

ok, i know it's never going to be spot on accurate.. but am struggling to figure out how it works out average mpg..

This is mainly due to the big changes that can happen following very short changes in driving stlye...

OK.. only picked the car up Monday ( 2.0 Diesel T-Spirit ) and filled it up monday night.

I work 50 miles away from home and 90% of that drive is on the Motorway - so just for giggles i have set the cruise control at 69 mph and sat there for most of the journey - which pushed my mpg up to the high 50's... which was nice.

I then dropped down to 5th, over took a lorry whilst going up a hill and the mpg had dropped to 52, back on with cruise and it crawled back up 56-57...

I'm wondering if the computer works my average mpg out over the last 10-15 miles only... or is it really every mile since last reset?

cheers.

[wastedagen]

ok, i know it's never going to be spot on accurate.. but am struggling to figure out how it works out average mpg..

This is mainly due to the big changes that can happen following very short changes in driving stlye...

OK.. only picked the car up Monday ( 2.0 Diesel T-Spirit ) and filled it up monday night.

I work 50 miles away from home and 90% of that drive is on the Motorway - so just for giggles i have set the cruise control at 69 mph and sat there for most of the journey - which pushed my mpg up to the high 50's... which was nice.

I then dropped down to 5th, over took a lorry whilst going up a hill and the mpg had dropped to 52, back on with cruise and it crawled back up 56-57...

I'm wondering if the computer works my average mpg out over the last 10-15 miles only... or is it really every mile since last reset?

cheers.

I always assumed, probably wrongly, that the average was worked out from the last time you reset it.

If i want a more accurate motorway average MPG then as soon as i am set at my speed, I press and hold the button while it's showing AVG MPG and it resets itself to 0. Briefly, then climbs right up to the 60's.

[Mooly]

It's a running total average. Drive for 5 miles at 50 mph and get around say 55mpg, then a quick squirt of acceleration and the average will drop dramatically. I think it recalculates every 10 seconds or so.

Do the same after having driven 500 miles at 55 mpg and it won't alter at all as the "average" is stil essentially the same. Only slowly would that figure creep down as you changed driving style.

For anyone that wonders "how" it knows how much fuel is used. It works it out indirectly. The fuel pressure gives a known rate of flow through each injector when it is open, so if you know how long each injector is open, you can calculate how much fuel has flowed.

[nurseydid12]

My 2.0 D4D was showing 29 mpg today. i was well p'd off! Is there something wrong with the car??

[tonycommander]

My 2.0 D4D was showing 29 mpg today. i was well p'd off! Is there something wrong with the car??

was that 'instant' or 'average' mpg ?

i see that you live in worcestershire too... I can make my car do very nearly 60mpg when i drive from malvern to birmingham every day for work - cruising at a mind numbingly dull 65 mph...

Whereas my wife can get low 30's when she takes the kids to school, and then pops up to her mums and then back to pick the kids up again - lots of short journeys (Especially up and down the hills) seems to totally kill fuel consumption.. probablly rightly too, as i seem to remember somewhere that short journeys in a diesel does not help...