Associated with the fuel controller of a supercharged diesel engine is a mechanism which limits the maximum fuel quantity in all operational states as defined by engine speed and air flow rate. This mechanism includes a three dimensional cam, displaced in rotation by a first transducer responsive to rpm or air flow rate and further displaced axially by a second transducer responsive to the other of these variables. A cam follower attached to the main fuel control rod of the controller makes contact with and follows the surface of the cam, thereby limiting the maximum fuel quantity admitted to the engine. Special provisions permit an enlarged starting fuel quantity and also permit corrections on the basis of further parameters, such as temperature. Several embodiments are presented.