Hi

I only have my car remapped about a month now but am noticing that it's MPG calculator is even more optimistic than before. It used to be about 4% optimistic, however now it's running at just on 7% optimistic.

Has anybody else noticed this after they got their vRS remapped?

Sorry in advance for the complete nerdiness of this thread!

Does anybody know exactly how the MPG is calculated?

Its a lovely smug feeling isnt it. When I had my 1.8T remapped my MPG dramatically improved with my other engine mods - still didnt stop the bloody car costing me £3k a year to run hence the switch to an oil burner !

I don't think my actual MPG has improved hugely. Its the on board computer that is now saying that I am doing more miles per gallon than I actually am (I brim to brim calculate every tank). It used to overestimate my mpg by about 2mpg, however I'm finding it can overestimate by nearly 5mpg now since I got it remapped.

Mines anywhere between 10 - 20% out

As to how it works it out, I'm sure it randomly selects a number between 40 and 60 each trip...

Has there been some sort of update to how these computers work out the MPG as mine is bang on +- 0.2 which can just be not filling the tank exactly same. surely the ecu knows how much fuel its putting in the engine or it wouldnt run right. i have also read another post saying someones computer trip is always 20% out. again mine is bang on the money.

I do 1000 miles per week and its always been right

I'm sure the average mpg is only for the trip (I know mine resets after a wile of being parked). So the MPG would not be for the entire trip, but for the section of driving running up to the filling up.

There are two modes to the computer - trip and lifetime. The trip calculations are automagically reset after two hours of the ignition being off and the lifetime ones are only reset when they hit xxxx miles (9999?) or xxx (99?) hours. If you reset the lifetime ones every time you fill up, you should get an average for the tank.

You can switch between them using the button under the stalk and you'll see the computer change the display from (1) to (2) and vice versa.

I'd always thought that the ECU had extremely accurate control over the fuel that was injected, but I guess that the mpg calculator may be based on some hard-coded "known" variables which are altered when the ECU is mapped but not reflected in the mpg calculator. It would be interesting to see how accurate the range predictions are compared to your actually miles per tank....

Chris

There are two modes to the computer - trip and lifetime. The trip calculations are automagically reset after two hours of the ignition being off and the lifetime ones are only reset when they hit xxxx miles (9999?) or xxx (99?) hours. If you reset the lifetime ones every time you fill up, you should get an average for the tank.

Yeh I reset the "lifetime" mode each time I fill up and then use the brim to brim method. At the next fill-up I cross reference the actual mpg with the mpg as indicated by the lifetime mode.

I'd always thought that the ECU had extremely accurate control over the fuel that was injected, but I guess that the mpg calculator may be based on some hard-coded "known" variables which are altered when the ECU is mapped but not reflected in the mpg calculator. It would be interesting to see how accurate the range predictions are compared to your actually miles per tank....

Chris

I never really bother noting this figure down as its dependent on your current driving style. So if you grannied it up to the garage, it might predict 600 miles but then floored it for the entire tank you might only get 300miles in reality.

There are two modes to the computer - trip and lifetime. The trip calculations are automagically reset after two hours of the ignition being off and the lifetime ones are only reset when they hit xxxx miles (9999?) or xxx (99?) hours. If you reset the lifetime ones every time you fill up, you should get an average for the tank.

You can switch between them using the button under the stalk and you'll see the computer change the display from (1) to (2) and vice versa.

I'd always thought that the ECU had extremely accurate control over the fuel that was injected, but I guess that the mpg calculator may be based on some hard-coded "known" variables which are altered when the ECU is mapped but not reflected in the mpg calculator. It would be interesting to see how accurate the range predictions are compared to your actually miles per tank....

Chris

I reakon that the miles of the mpg calculation are taken from the speedo distance, so with that taken into account I think thats why the mpg is out.

Off topic but how do you reset the lifetime values?

Off topic but how do you reset the lifetime values?

Set the display on MPG, press RESET to get the 'lifetime' MPG displayed then press and hold RESET for 2/3 seconds.

Does the computer compensate for the increased boost etc. that a remap brings? Or does it still think it's standard... that might account for some discrepancies?

What's this lifetime mpg and how do I view it btw?

But surely all it needs to know is the amount of fuel being injected (which it should know if the remap changes to inject more) and the distance the car has travelled? Would be interesting to know exactly how it was calculated....

As for the lifetime figures, you can switch between them and journey by pressing the RESET button briefly on the underside of the stalk and you'll see the (1) change to a (2) or vice versa - I forget which way round they are. Holding the RESET button in for a few seconds will reset whichever figures (lifetime or journey) are shown at the time.

Chris

My PD130 Ibiza is consistently 3% optimistic