Firing order is the sequence in which a multi-cylinder engine ignites fuel in each cylinder, and it matters because the wrong sequence causes misfires, vibration, and engine damage.
Every gasoline engine with more than one cylinder needs its spark plugs to fire in a specific order. That order is determined by the engine's design — the arrangement of cylinders, the crankshaft, and the distributor or ignition coil pack. If cylinders fire out of sequence, the engine cannot produce smooth power, and you will feel rough idling, hesitation, and loss of fuel economy.
The firing order is not something you choose or change. It is built into the engine when it is manufactured. But understanding what it is helps you diagnose ignition problems, replace spark plugs in the right order, and know what a mechanic is talking about when they mention it.
Key Takeaways
- Firing order is the sequence in which cylinders ignite, determined by the engine design and the position of the crankshaft and distributor.
- Common firing orders for four-cylinder engines are 1-3-4-2 or 1-2-4-3, and for eight-cylinder engines are 1-5-4-8-6-3-7-2 or 1-8-4-3-6-5-7-2.
- Spark plug wires or coil packs must be connected in firing order, and connecting them wrong causes misfires and rough running.
- You can find your engine's firing order in the owner's manual, on a label under the hood, or from a repair manual for your specific year and model.
How firing order is built into engine design
The firing order is determined by three physical facts about your engine: the number and arrangement of cylinders, the shape and timing of the crankshaft, and the position of the distributor or ignition coil pack. Manufacturers choose a firing order that spreads power strokes evenly around the crankshaft so the engine runs smoothly and the load on bearings is balanced.
For a four-cylinder engine, the cylinders are usually numbered 1, 2, 3, 4 from front to back (or sometimes front to back on one side, then back to front on the other, depending on the engine layout). The crankshaft has lobes that push the pistons down in a specific sequence. The distributor or coil pack is timed to send spark to each cylinder in the order the crankshaft dictates.
Once the engine is built, the firing order cannot be changed without redesigning the crankshaft and distributor — which is not practical. The firing order is fixed for that engine model and year.
Common firing orders by engine type
Four-cylinder engines typically use one of two firing orders: 1-3-4-2 or 1-2-4-3. The first number is always cylinder 1, which is the reference point. The sequence tells you which cylinder fires next, then next, and so on. Both sequences spread the power strokes evenly and are equally common depending on the manufacturer and engine design.
Six-cylinder engines often use 1-5-3-6-2-4 or 1-2-3-4-5-6, again depending on the crankshaft design. Eight-cylinder engines are more varied. Common orders include 1-5-4-8-6-3-7-2 and 1-8-4-3-6-5-7-2. V-shaped eight-cylinder engines (V8s) use different orders than inline eight-cylinders, which are rare in modern cars.
The only way to know your engine's firing order is to check the owner's manual, look for a label on the engine block or under the hood, or consult a repair manual for your specific year, make, and model. Do not guess or assume it matches another car you own.
Why firing order matters when replacing spark plugs or ignition wires
When you replace spark plugs, you remove and install them one at a time, and the order does not matter — each plug goes back in its own cylinder. But when you replace spark plug wires (on older cars with a distributor), you must connect them in firing order. If you swap two wires by mistake, those two cylinders will fire at the wrong time, and the engine will misfire and run rough.
On newer cars with coil packs (one coil per spark plug, mounted directly on the plug or nearby), each coil is wired to a specific cylinder. If you disconnect and reconnect coil packs, you must put each one back on the correct cylinder. Swapping them causes the same misfires.
The safest approach is to remove and replace one wire or coil at a time, so you never have to remember which wire goes where. If you do remove multiple wires, label them with tape before you take them off, or take a photo of the engine before you start work.
What happens when firing order is wrong
An engine running out of firing order will not start, or will start and when ready stall. If it does run, you will feel a rough, uneven idle — the engine shakes and sounds like it is missing. Under acceleration, the car hesitates and lacks power. Fuel economy drops because the engine cannot burn fuel efficiently.
Over time, running out of firing order can damage the catalytic converter (because unburned fuel enters the exhaust), foul spark plugs, and strain the engine mounts. The check engine light will come on, and a scan tool will show misfire codes for one or more cylinders.
If you suspect firing order is wrong — usually after you have worked on the ignition system — the fix is to trace each wire or coil back to the correct cylinder using the firing order sequence and the owner's manual or repair guide.
How to find your engine's firing order
The owner's manual is the first place to look. Open it to the engine specifications section, and the firing order is usually listed there along with spark plug type and gap. If you do not have the manual, check under the hood for a label or sticker on the engine block, valve cover, or air intake — many manufacturers print the firing order there.
If neither source is available, a repair manual for your specific year, make, and model (such as a Haynes or Chilton manual, available in print or online) will have the firing order in the engine section. You can also search online for "[your year, make, model] firing order" and find it on automotive forums or repair sites, but always verify it against a manual if possible.
Write down the firing order and keep it with your car documents. If you ever work on the ignition system or need to explain the problem to a mechanic, having the correct firing order on hand saves time and prevents mistakes.
Firing order versus ignition timing
Firing order and ignition timing are related but different. Firing order is the sequence in which cylinders ignite — cylinder 1, then 3, then 4, then 2, for example. Ignition timing is when each cylinder ignites relative to the position of its piston — measured in degrees before or after the piston reaches the top of its stroke.
Both must be correct for the engine to run smoothly. Firing order is fixed by the engine design. Ignition timing can be adjusted on older cars (by turning the distributor) or is controlled by the engine computer on newer cars. If the engine runs rough, the problem could be wrong firing order, wrong ignition timing, or both — a mechanic can diagnose which one using a timing light and a scan tool.
Frequently Asked Questions
Can I change my engine's firing order?
No. Firing order is determined by the crankshaft and distributor design and cannot be changed without rebuilding the engine. If your engine is running out of firing order, the problem is a wiring or connection mistake, not the engine itself.
What does a misfire code mean?
A misfire code means one or more cylinders did not ignite on schedule. The cause could be a bad spark plug, a loose or swapped ignition wire, a faulty coil pack, low fuel pressure, or a timing problem. Check firing order first if you recently worked on the ignition system.
Do all four-cylinder engines have the same firing order?
No. Four-cylinder engines commonly use 1-3-4-2 or 1-2-4-3, but some use other sequences. Always check your owner's manual or repair guide for your specific engine — do not assume it matches another car.
Why is cylinder 1 always first in the firing order?
Cylinder 1 is the reference point by convention. The manufacturer numbers cylinders starting from one end of the engine, and the firing order always begins with cylinder 1 and lists the rest in sequence. This makes it easier to communicate and document the order.