By far the easiest way, is to obtain a workshop manual for your particular vehicle.
Click the link:
firing order is on top of the manifold (if it is stock).
Firing order is 1-3-4-2.
The firing order diagram for this car is found in its owners manual. It is also found in the maintenance and repair manual book as well.
Google it
Click the link.
1-2-3-4-5-6- weird firing order
at autozone. just ask
what is the firing order & leads for a landrover discovery 1991 3.5 v8i duel fuel
the best answer I can give you is to go to http://www.autozone.com. Enter your vehicle info and go to "specifications". You will be able to find the firing order in a diagram there.
autozone.com
depends on RPMs
On Google