The three cylinders will be firing in consecutive order, either front to back or back to front. Take what ever "firing order" is given in the specs and write it down consecutively several times. In this case it is:View attachment 8286
Maybe something like this?
1 3 2 1 3 2 1 3 2 1 3 2
Notice the order of 321 repeatedly. This is the order from back to front. Firing orders are always given starting with number 1 cylinder, but since it is repeated, the actual order the engine is running at, can start at any point.