MUFFLER 2Y3391 - Caterpillar

Many dealers and servicemen have desired more information about differences in timing advance specifications as shown in Service Manuals, Special Instructions, and Fuel Setting Information (Microfiche and/or Charts). These differences are the result of engine design and/or fuel system characteristics.
Complete details about fuel system characteristics and timing advance specifications are given in Special Instruction Form SMHS6964-01, "Using The 1P3500 Or 2P8280 Injection Timing Groups". In addition to specifications for the automatic timing advance, Page 15 of this form gives an explanation of fuel injection characteristics and other timing advance factors. Other publications generally do not give complete information about all the factors that have a relation to fuel injection timing. Some show only the degrees of automatic timing advance. Also, while timing advance is normally given in degrees of crankshaft rotation, some publications show the automatic advance in degrees of camshaft rotation, which is one-half that of crankshaft rotation. Before timing information is used, be sure you know if it is given in crankshaft or camshaft degrees.