What action is taken when one CMP isn't functioning on a composite engine?

When one camshaft position sensor (CMP) is not functioning on a composite engine, fully retarding the timing is the correct action to take. In an engine, the CMP sensors provide critical timing information for the engine's ignition and fuel injection systems. If one of these sensors fails, it can lead to incorrect timing adjustments which may affect the engine's performance.

Retarding the timing helps to prevent potential engine knocking or pinging that can occur if ignition occurs too early in the combustion cycle due to improper sensor signals. By retarding the timing, the engine management system compensates for the faulty signal to stabilize performance and protect the engine components from damage.

In contrast, fully advancing timing or making changes to the air-fuel ratio, such as going rich or lean, would not address the malfunction of the CMP. Advancing timing could exacerbate issues related to pre-ignition or detonation, while changing the air-fuel mixture can lead to further complications with emissions and engine performance. Thus, retarding the timing serves as a safer adjustment when dealing with a nonfunctioning CMP in an engine.