There's no 4.0L six-cylinder engine in a Ford Ranger. The Ford Ranger, depending on the year, used various V6 engines (like the 3.0L and 4.0L Cologne V6s in older models or the 3.2L and 3.7L V6s in newer ones), but *never* an inline-6. Inline-6 engines are much less common in trucks.
Therefore, the question of a firing order for a "four liter 6 cylinder Ford Ranger" is moot. You'd need to specify the *exact* engine and year of the Ranger to get the correct firing order.
