The diesel engine produces the pulse for the tacho in a different way from the petrol engine, so its gonna confuse the digital dash. Take a look HERE for more info.
Contact Dom as the guy is a genious with these dashes and he can sort it for you.

transponder unit is probably the wrong one i belive, think there is bout 3 diffrent ones.

in the process of wirin in my dash and for some reason the rev counter isent givin a true reading,says 5000rpm at standstill,it works properly apart from that and shoots off the scale when i tap the pedal tho,any idea whats doin this? is it a td problem? cheers woody