After troubleshooting per the Boeing Fault Isolation Manual (BFIM) and changing a right Rudder Ratio Change Module on a B767-300 for a Rudder Ratio EICAS message; Mechanic feels a note should be added to the BFIM to also reference the maintenance manual chapter for RII requirements.

Narrative

Flight on Feb/09; ground interrupted and returned to the gate with a Rudder Radio message on the EICAS. I looked up the fault message in the Boeing Fault Isolation Manual (BFIM) and found reference 27-21-00 Rudder Ratio Light illuminated on the ground/inflight EICAS message 'Rudder Ratio' displayed. I followed the Fault Isolation Manual and found the right-hand Rudder Ratio Change Module had failed. I ordered up the part and checked effective in the IPC reference 27-09-01. I did a keyword search in the Aircraft Maintenance Management 'Rudder Ratio.' I found several results for rudder ratio; but none of them were for the removal and replacement (R&R) of the rudder ratio change module. I decided to use Chapter 20 of the Wiring diagram to change the RRCM and performed the FIM task 27-21-00. The test passed and the message on the EICAS disappeared. I signed the logbook; inspected and found Right-hand Rudder Ratio Change Module Failed fault ball; removed and replaced per maintenance manual operations checked good. After the airplane departed; I did some more research and found a reference under rudder and rudder trim control system adjustment/test; maintenance manual 27-21-00. I failed to read this maintenance manual reference and see that the operations check was an RII item. The test was completed as described in the maintenance manual; but no one else besides the pilots witnessed the operations check to sign an RII. I feel a note should be put I the BFIM to direct the Mechanic performing the task if he changes the RRCM due to a fault with the RRCM to follow the maintenance manual and give the maintenance manual reference. Callback conversation with Reporter revealed the following information: reporter stated he was told the Required Inspection Item (RII) he thought he had missed; after changing the Rudder Ratio Change Module in the E/E electronics compartment; was in fact; not required after all. Because he had changed the Ratio Change Module box and had not actually broken into; the rigging or any part of the rudder cable or trim system; an RII was not required. Reporter stated he still feels some reference to a maintenance manual chapter should be included in the BFIM; in case an RII is required; especially for flight control systems.