5 mpg - maxxed out the MFD!

[Hairy Porter]

Instant mpg readings are fairly meaningless. They are only really useful when you are cruising under constant throttle. As the computer is probably just looking at intake manifold pressure, all it really tells you is how wide open you've got the throttle and how much load the engine is under. With the accelerator nailed and the load of pushing a car through the air at 100+ I'm not surprised you only get 5mpg - at that instant and under that set of conditions.

Average mpg read after covering a reasonable distance gives you a more meaningful (if slightly optimistic) value.

The computer knows exactly how much fuel is squirted into the engine.  It controls the squirters.  Even things like battery voltage are taken in to account to achieve precise control of the fuel use.  The readout is spot-on.

[jdjd]

Im tight i watch constently how much fuel im burning. Seems like after a quick blast u can c the needle visably drop.

[FroGTI]

OK, in the name of science (and fairness) I did an economy run this afternoon of about 20 miles and managed 43mpg. No breaking the speed limit and only one quick burst of speed to overtake a couple of other road users.

I guess I'm just not used to petrol cars yet: my (remapped) 330d also got 43mpg when I drove carefully and about 35 when I wanted a bit of fun. The GTI seems to go from 43 down to about 18

[matchboy]

OK, in the name of science (and fairness) I did an economy run this afternoon of about 20 miles and managed 43mpg. No breaking the speed limit and only one quick burst of speed to overtake a couple of other road users.

I guess I'm just not used to petrol cars yet: my (remapped) 330d also got 43mpg when I drove carefully and about 35 when I wanted a bit of fun. The GTI seems to go from 43 down to about 18

that sounds about right you know - i've been getting 36 odd when driving normally (so you're 43 sounds right given the revo spiel of higher economy) yet when i've put my foot down and had some fun the average goes down to 22 (again, in line with your 18 - as i'm assuming you're using more petrol).

[mac7]

The computer knows exactly how much fuel is squirted into the engine.  It controls the squirters.  Even things like battery voltage are taken in to account to achieve precise control of the fuel use.  The readout is spot-on.

On what information are you basing that explanation? The ECU computer specifies how long to open the injectors based on its fuel map, but the little screen you are looking at on your dashboard is a separate computer. To my knowledge the ECU does not record the volume of fuel which has passed through the injectors, so can not provide that data to the multi-function display.

[R32UK]

OK, in the name of science (and fairness) I did an economy run this afternoon of about 20 miles and managed 43mpg. No breaking the speed limit and only one quick burst of speed to overtake a couple of other road users.

I guess I'm just not used to petrol cars yet: my (remapped) 330d also got 43mpg when I drove carefully and about 35 when I wanted a bit of fun. The GTI seems to go from 43 down to about 18

that sounds about right you know - i've been getting 36 odd when driving normally (so you're 43 sounds right given the revo spiel of higher economy) yet when i've put my foot down and had some fun the average goes down to 22 (again, in line with your 18 - as i'm assuming you're using more petrol).

Yep I would agree with that. Tootling along I can get upwards of 40mpg quite easily on a longish journey (99 Ron of course). However giving it a good blast will easily get it down to below 20mpg on a short run. So very good when you want them to be... not so good when your pressing along. I can live with that

[Hairy Porter]

The computer knows exactly how much fuel is squirted into the engine.  It controls the squirters.  Even things like battery voltage are taken in to account to achieve precise control of the fuel use.  The readout is spot-on.

On what information are you basing that explanation? The ECU computer specifies how long to open the injectors based on its fuel map, but the little screen you are looking at on your dashboard is a separate computer. To my knowledge the ECU does not record the volume of fuel which has passed through the injectors, so can not provide that data to the multi-function display.

It does.