instrument cluster mis-readings after dash replacement?

[camcc]

replaced my dash yesterday......and when putting it all back in (what a job) i realised that one of the brackets on the instrument cluster (rev and speedo) was snapped and it wouldn't go in right, so I took the cluster shell out of a 325, swapped the clocks and the SI board (I think) and it all went in nicely.

I have noticed however that the fuel consumtion dial, which I live by (boring I know) is showing considerably lower figures .ie 20 on the motorway when it used to be 30 and I can only get 25 round town rather than the 30 I used to get (really light foot)

and after that essay....my questions is...what could be causing this as all other dials work without issue??

[ad318i]

did you change the decoder part as well?? on the front of the cluster

[camcc]

is that the little white thing that just clips out? tbh I can't remember, I was doing it with the help of someone else and it was a bit of a muddle to be honest as we had three different clusters apart at the same time

Why would a different decoder show different consumption? Will it, over time, re-program to my cars stats?

[Brianmoooore]

You need the coding plug from your original cluster, and no, it won't adapt.
You only need to remove thr trim to change it.