An engine-controlling unit/method for an internal-combustion engine with first and second combustion-chamber groups having a first and second catalytic exhaust-gas converter, respectively, having (a) a master control device that controls a combustion-air ratio for the first combustion-chamber group by forcibly exciting the first combustion-chamber group, further having (b) a slave control device that controls a combustion-air ratio for the second combustion-chamber group by forcibly exciting the second combustion-chamber group, and further having (c) a data link between the master and slave for control through the master. It is proposed (d) for the master to transmit a synchronizing signal to the slave over the data link during changeover between the rich and lean combustion-air ratio within the scope of forced excitation, and (e) on receipt of the synchronizing signal from the master for the slave to change over within the scope of forced excitation between the rich and lean combustion-air ratio.