The firing order for a 1991 Ford Ranger's coil pack depends entirely on the engine it has. Ford Rangers of that year came with several different engines (2.3L 4-cylinder, 2.9L V6, and a 4.0L V6 being the most common). Each engine has a different firing order.
You MUST specify the engine size (2.3L, 2.9L, or 4.0L) to get the correct firing order.
Once you provide the engine size, I can look up the appropriate firing order and explain how the coil pack relates to that sequence.
