Did do a change on an ecu a while ago, and the dud one had injector fault written on it. Dont know whether thats relevant or not, might be the time to get Fiat to do a diag on it.
Tony.
Is the injector light on? It could be a faulty injector, which seems to be a favourite on this engine. If you have a trawl through the search engine, there's a thread somewhere with a simple explanation by Jug on how to check for a faulty injector.
Mine did the same, turns out one of the spark plugs died so the other three were doing all the work causing injector problems. Check these before you do anything else as it could be a cheap solution!
hum we just had a multiple 1.6 16v at work very similar engine and ecu and it seems that a dodgy lead plug or coil can feed back to the ecu and make it think theres an injector down cos we had one saying multiple injectors down and a new coil solved it
it also caused dash to go nuts when reved and the missfire was most prominent very weird
and ontop of that there common for injectors
they were never the best of engines well the engine was fine very powefull very revy but the electrics fueling and ignition was a disaster