depends how badly blown the ecu is. most comon faiulure on the digi ecu is down to poor gearbox earth. this causes ecu to short injectors to ground, though the spark usually works ok still, anmd so rev counter still jiggles.
if ecu completly exploderised then rev counter wont jiggle, as ecu wont be telling coil to spark and so rev counter has no signal to detect
