I'd like to do something with my P1's speedo to make it more accurate as it's currently over 10% optimistic and I assume this will affect the odometer reading as well, thus I'll have covered more miles than I actually have. I am running 215 40 17's, before that I had 215 45 17's and it was still 10% out.

I have looked into doing it and it looks like I can put a yellow box (Official home page of the Yellow Box Speedo Recalibrator) in line with the speed sensor cable. But, has anybody else done this as I hate being a guinea pig!
Or, is there a more elegant solution - i.e changing software value in the ECU for example?

Thanks,

Jon

 

Obvious question, does it overread by a percentage or a fixed offset (i.e. does it always read around 10mph fast)? If it's always out by the same sort of number the easiest way to fix it is simply to pull the needle off the front of the speedo driver and reposition it slightly.

When you say it's over 10% over, what are you comparing it with, GPS?

Unfortunately not. You can change the way the ECU calculates road velocity, but it wouldn't do you any good in this instance. The instrument pack doesn't receive the calculated velocity from the ECU, it gets the raw signal from the pulse generator on the gearbox and converts it internally.

To alter the main ECU reading by a percentage, you need something that rescales the pulses. While I've no personal experience of that "Yellow Box", it looks from the website like it'll get you where you want to be.

 

Hi,

Thanks for the reply.
Yes it over-reads by a percentage figure, at 70 MPH on speedo, GPS says I'm travelling at 62 MPH, at 60MPH on speedo, GPS has 53MPH. At 40 MPH on speedo, GPS has 35. So it looks like it's about 12% over read on the speedo.

I'll look into getting a 'yellow box' to see if that can sort it out.

Jon

 

[QUOTE=Splitpin;9215828]Obvious question, does it overread by a percentage or a fixed offset (i.e. does it always read around 10mph fast)? If it's always out by the same sort of number the easiest way to fix it is simply to pull the needle off the front of the speedo driver and reposition it slightly.

when my car is running and sitting still i have noticed it does read 10mph.


splitpin oh world of knowledge,

i have a problem with my spedo reading 10mph over so much so my ecu thinks i'm doing 10mph when standing still (so my launch control won't work) i thought i had connected the black wire on the speed convertor the wrong way round but would you say if i moved my speedo needle it would sort my issue ?

i have a v4 my98 import.

thanks if you can help.