How are the cylinders numberd on a 1990 2.9l engine?

The firing order for a 1990 2.9L V6 engine (typically found in Ford vehicles) is 1-5-3-6-2-4. Cylinder numbering usually starts at the front of the engine on the passenger side (right side in the US). However, always double-check your specific engine's markings as there might be slight variations depending on the exact application. A diagram in your owner's manual or a readily available online parts diagram will confirm the cylinder numbering for your specific vehicle.