Hi I've just bought a spider tuning box for my 2016 vrs 184, apparently I have to recalibrate the mpg ratio via a OBD2 , can anyone throw a bit of light on this subject please .

You need VCDS or OBDEleven to change a parameter. Do you have access to either?

Yeah I have a carista

This is how you do it with VCDS:

 

well in theory 100% would be the correct number. Why add 110? This does not look like a calibration.

102% is correct from my testing, 100 is a little out. I run 2+2 on my DTUK box and I find 109% to be pretty much accurate

I put 110% and it is quite correct.

I'll have to test if 111% would work.

Looks like I'll go with 110% and see how it goes, (not that I would know if it is right or wrong though) I'm still unsure of the reasons why it needs to be change! 

You don’t need to change it, you can just accept that it’s going to be wrong. It’s because the box fools the ECU into sending more fuel pulses than it thought it was providing so the MPG reading will overread.

So basically whats happening ?
With the tune box, is the actual fuel consumption SHOWN in the dashboard going up or down ?
 

I'm quite interested in this also - not because I've had a remap, but just because my MPG display is wrong.

 

So, if it's set at 100%, and the average displayed is 55mpg but the actual figure is 50mpg: what do you do?

I guess you'd need to set the VCDS thing to 90 or 91%?

 

 

Other way, 104% is usually correct for a standard car.

and with DTUK ? 110% ?

I found 107 was good but on the vc it’s too far the other way, 104 is good on my vc with DTUK box set to 1+2

On 03/03/2019 at 17:48, fat4l said:

So basically whats happening ?
With the tune box, is the actual fuel consumption SHOWN in the dashboard going up or down ?
 

With a box the shown fuel consumption drops ie the numbers go up = wrongly indicating better fuel consumption. The reason is they are a bit of a bodge. They take the correct common rail fuel pressure and convert it to an incorrect lower than actual reading. The ECU then takes this as gospel and increases the common rail pressure to what it thinks is correct, actually is far higher. More pressure = more fuel. So more fuel is going in at the same throttle position, the driver lifts off to compensate and thats where the computer is fooled, it thinks less fuel is going in because the driver has lifted off for the same power, when  actually it is the same. The inaccuracy of the fuel consumption indicator is directly proportional to the % of common rail pressure increase or correction by the box. Some remaps do the same if they mess with the fuel pressure. But they generally increase boost pressure  which is why they are superior. Ive had a couple of boxes in the past which only increased fuel pressure and gave incorrect fuel consumption numbers. Iv'e not come across a box that actually controls more functions but I know they are out there, just not interested in them. Bluefin every time for me if I bother at all. I asked a box provider years ago to explain to me how a box has a map when it is dumb to what is going on everywhere apart from the fuel pressure. They couldn't explain it. I am not saying they don't have maps with more sophisticated versions now or are available with maps.

 

Would still like someone to explain how an analogue connection to a fuel pressure sensor enables a  box to provide a variable map that isn't just a pressure raised copy of the original ? I thought of things like it knows what fuel pressures are used at certain times and works with them, but it doesn't stack up.