Cylinder Numbering vs. Firing Order
The difference between a cylinder's permanent number and the repeating sequence of combustion events, and why compression TDC is not just "the timing mark at zero".
These two ideas are constantly confused, and the confusion causes real damage — a misfire code names a cylinder, not a position in the firing sequence.
Two different things
Cylinder numbering tells you each bore's permanent identity. Firing order tells you the repeating sequence of combustion events. The crankshaft makes two full revolutions during a four-stroke cycle, so checking only that the timing mark is at top dead center is insufficient: cylinder 1 can be at compression TDC or exhaust TDC. Both valves should be closed at compression TDC.
Bank numbering conventions differ between manufacturers, so a V8 that looks identical from above may number its cylinders in a completely different order from one you worked on last week. Confirm it from the diagram for that engine family rather than from memory.
Working method
Mark the banks temporarily when working in a crowded engine bay. Route one connection from its source to its cylinder and verify both ends before starting the next; tracing a completed bundle afterward invites transposed pairs.
Values, sequences and intervals are vehicle-specific. Use the specification page for your exact year, engine and component alongside this procedure, and follow the manufacturer document it cites.
Cylinder Numbering vs. Firing Order FAQs
Does P0304 mean the fourth cylinder in the firing order?+
No. It refers to physical cylinder 4. Misfire codes always name the cylinder by its permanent number, never by its place in the firing sequence.
Is cylinder numbering the same on every V8?+
No. Bank numbering conventions differ by manufacturer and sometimes by engine family. Use the diagram for the specific engine.
Is cylinder numbering the same as firing order?+
No. Numbering identifies physical cylinders; firing order is the sequence in which those cylinders begin power strokes.
Can a camshaft change the firing order?+
On engine families offered with alternate orders, yes. A camshaft and its matching ignition routing must use the same order.