What is the firing order of ignition timing?

There is no single universal firing order; it depends on engine design. For example, inline-4 configurations commonly use 1-3-4-2, inline-6 often follows 1-5-3-6-2-4, and many V8 engines use 1-8-4-3-6-5-7-2. In addition, ignition timing concerns when the spark fires within the piston cycle, typically measured in degrees before or after top dead center (BTDC/ATDC), and is adjusted by the engine’s control system for optimal performance. This article explains the firing order, how ignition timing differs, and how to verify your engine’s specifications.

Firing order refers to the sequence in which each cylinder receives a spark and completes its power stroke. Ignition timing, on the other hand, is the exact crankshaft position at which that spark occurs. While related, these are two separate aspects of ignition systems that together influence power, smoothness, efficiency, and emissions. Below, you’ll find typical patterns by engine layout, plus guidance on how to determine and verify the exact specifications for your vehicle.

Firing order by engine configuration

Below are representative firing orders used in common configurations. Always confirm your exact engine’s order from the service manual or the engine block/cylinder head markings, as there are many variants among manufacturers and model years.

• Inline-4: 1-3-4-2


• Inline-6: 1-5-3-6-2-4


• V8 (example widely used in GM small-blocks and many others): 1-8-4-3-6-5-7-2

These examples illustrate how firing order patterns differ with engine layout. Variants exist even within the same configuration, so always verify the exact sequence for your engine.

Ignition timing: what it is and why it matters

Ignition timing is the precise crankshaft position at which each spark plug fires. It is usually expressed in degrees of crank rotation before TDC (top dead center) or after TDC. Advancing timing means firing earlier in the compression stroke; retarding timing means firing later. Proper timing maximizes power and efficiency while avoiding engine knock. Modern engines typically use an electronic control unit (ECU) to adjust timing dynamically based on RPM, load, temperature, and other sensors.

How to verify and set the firing order and timing

To ensure correct operation, verify both the firing order and the ignition timing with the vehicle’s official specifications. The steps below are general guidelines and should be supplemented by the exact manufacturer procedures for your engine.

• Consult the service manual or OEM data to confirm the firing order and cylinder numbering for your specific engine.


• Inspect markings on the engine if available; some blocks or valve covers have stamped firing-order diagrams.


• If your engine uses a distributor, verify the rotor orientation and cap connections align with the correct cylinders in the firing order.


• For coil-on-plug systems, rely on the ECU’s timing maps and diagnostic procedures to ensure proper timing.


• Use a timing light and a vacuum gauge as needed to check idle timing and adjust within manufacturer-recommended ranges, if applicable. Modern engines may require dealer-level diagnostic tools or software.

Always avoid making timing adjustments beyond the manufacturer’s specified ranges, as excessive advancement or retardation can cause engine damage, reduced performance, or increased emissions.

Summary

The firing order is the predetermined sequence in which cylinders ignite, and it varies by engine configuration. Ignition timing specifies when in the engine cycle the spark fires and is separate from the firing order, though both affect performance and safety. By consulting the correct manuals, inspecting engine markings, and following proper diagnostic procedures, you can ensure your engine fires in the right order and with timing that keeps it running smoothly and efficiently.

Further reading

For deeper guidance, refer to your vehicle’s service manual, OEM ignition system documentation, and reputable automotive engineering resources that cover firing orders, timing curves, and modern ECU-based timing strategies.

Is ignition timing before or after TDC?

Ignition timing (or spark timing) controls when the spark plug fires during the Compression Stroke. Ignition timing is measured in degrees of crankshaft rotation, before top dead center (BTDC). In a perfect world, The spark plug fires.

What firing order is 1 8 4 3 6 5 7 2?

The firing order 1-8-4-3-6-5-7-2 is a common sequence for many V8 engines, particularly Chevrolet, AMC, Buick, and Chrysler models, designed to ensure engine balance and reduce vibration. This order dictates the sequence in which the cylinders fire, and for many V8 engines, the distributor rotates clockwise with this firing order.
 
You can watch this video to learn about the 4/7 firing order swap in camshafts: 57sDavid FreiburgerYouTube · Jan 22, 2020
How it works

• Sequence of ignition: The firing order is the sequence of which cylinders ignite one after another. 
• Engine balance: This specific order is used to distribute the power strokes evenly across the crankshaft, which helps to prevent excessive vibration and stress on the engine. 
• Manufacturer variations: While 1-8-4-3-6-5-7-2 is a very common firing order for many V8 engines, other manufacturers use different sequences. For example, most Ford V8s use a 1-5-4-2-6-3-7-8 order, and some modern GM LS engines use 1-8-7-2-6-5-4-3, notes this OnAllCylinders article. 

This video explains the V8 firing order and cylinder numbering: 59sBad Influence GarageYouTube · Jan 4, 2021

What is the correct firing order?

Straight-Four Engines: Straight four engines often follow a firing order of 1-3-4-2, though some British engines use 1-2-4-3. Flat-four Engines: Flat-four engines use the firing order of R1-R2-L1-L2. Straight-Five Engines: Straight-five engines employ the firing order of 1-2-4-5-3 to minimise primary vibrations.

What does firing order 1-3-4-2 mean?

1-3-4-2: This firing order is commonly found in inline -four engines, where the cylinders are arranged in a straight line. The spark plugs ignite the fuel-air mixture in the following order: cylinder 1, cylinder 3, cylinder 4, and finally cylinder 2.