Abstract: The disclosure illustrates a means for automatically controlling the operation of a cylinder deactivating system in a multicylinder compression ignition engine which system is intended to increase the load on the cylinders that have not been deactivated. The control means is responsive to coolant pump output pressure which varies directly as engine rpm varies. The cylinder deactivating system functions either by cutting off the flow of fuel to the injector for each deactivated cylinder or cylinders or by actuating an engine brake system. The control means automatically stops the operation of the cylinder deactivating system when engine rpm increases to the point that the coolant pump output pressure exceeds a threshold level. This prevents any possibility of injector scuffing or loss of power at higher rpm.