Corsa-B.uk - Vauxhall, Opel and Holden Corsa B Owners Club

i have had a 1995 1.4 16v corsa and i have changed the engine to a 1.6 16v, which fitted nicely, but the only problem i have had is that it only revs to 4.8, when the managment light is on but it revs to 6.5 before it comes on. i have had the car put on to a computer and it came up with the knock sensor which i have put a new one on but didn't make any difference.
Does anyone have any idea what it could be cheers

did u change the ecu

silly question but possible