The ECU is the fuel injection system's brain simple as. All Cinqs made from 1995 onwards use the Marelli Weber 16F ECU model of these, so If the ECU in the Sporting produces a pulse for a tacho, so will an ECU in an 899cc!.
But still, a lot of tachometers take a feed from the ignition coil..problem is, most 4 cyl engines use 1 coil for all the cylinders, but the Cinq nicely uses 2, so it (the system) produces half the number of pulses than a typical system.
Tom (AofB)
GrpN Catback Exhaust system is here...just need to get the bleeder on now!!