The LS engine fires its cylinders in a specific sequence: 1-8-4-3-6-5-7-2

The firing order is the sequence in which each cylinder ignites its fuel mixture. In an LS engine, that sequence is 1-8-4-3-6-5-7-2, and it never changes — it's built into how the engine's crankshaft and camshaft are designed to work together. This particular order matters because it balances the forces inside the engine, keeps the crankshaft spinning smoothly, and distributes heat evenly across the engine block.

If you're rebuilding an LS, swapping one into another vehicle, or troubleshooting a misfire, knowing this sequence helps you connect spark plug wires, coil packs, and fuel injectors in the right order. Get it wrong, and the engine won't run — or it will run badly, misfiring and shaking.

Key Takeaways

  • LS engines fire cylinders in the order 1-8-4-3-6-5-7-2, which is determined by the crankshaft and camshaft design and cannot be changed.
  • Cylinder numbering on an LS starts at the front of the engine on the driver's side (cylinder 1) and alternates sides as you move toward the back.
  • Spark plug wires, coil packs, and fuel injectors must follow this firing order, and connecting them incorrectly will cause the engine to misfire or not start.
  • The firing order is the same across all LS variants — LS1, LS2, LS3, LS7, and others — because they share the same basic crankshaft design.

How LS cylinder numbering works

Before you can use the firing order, you need to know which cylinder is which. On an LS engine, cylinder 1 is at the very front of the engine on the driver's side. From there, the numbering alternates: cylinders 1, 3, 5, and 7 are on the driver's side, running front to back. Cylinders 2, 4, 6, and 8 are on the passenger side, also running front to back.

This layout is standard across all LS variants. If you're looking at the engine from the front of the vehicle, you'll see the driver's side cylinders on your left and the passenger side on your right. Knowing this layout prevents confusion when you're routing spark plug wires or installing coil packs.

Why the firing order is 1-8-4-3-6-5-7-2

The firing order isn't random — it's engineered into the crankshaft and camshaft geometry. The crankshaft has eight throws (one for each piston), and they're positioned at specific angles. The camshaft opens and closes the intake and exhaust valves in a sequence that matches those angles. Together, they determine which cylinder fires when.

This particular sequence spreads the power strokes evenly around the crankshaft, which keeps the engine balanced and running smoothly. If cylinders fired in numerical order (1-2-3-4-5-6-7-8), the crankshaft would experience uneven loading and vibration. The actual sequence distributes the load more evenly, which is why engineers chose it.

Connecting spark plugs and coil packs in the right order

Modern LS engines use coil-on-plug ignition — each spark plug has its own coil pack mounted directly on top. The engine's computer controls when each coil fires, and it follows the firing order 1-8-4-3-6-5-7-2. If you're installing a new set of coil packs or replacing spark plugs, the physical location of each coil doesn't matter as much as making sure the engine's wiring harness connects each coil to the right cylinder.

If you're converting an older LS engine that used a distributor and spark plug wires, the wires must follow the firing order around the distributor cap. Starting at the terminal connected to the coil, the wire positions going clockwise (or counterclockwise, depending on the distributor) should be 1-8-4-3-6-5-7-2. Swapping even two wires will cause a misfire in those cylinders.

Fuel injector timing and the firing order

Fuel injectors also follow the firing order, though less obviously than spark plugs. The engine's computer opens each injector just before the spark plug fires in that cylinder, so the fuel and air mixture is ready to ignite. The injector wiring harness is labeled to match specific cylinders, and connecting them out of order won't prevent the engine from starting — but it will cause rough idle, hesitation, and poor fuel economy because cylinders are being fed fuel at the wrong time.

If you're swapping an LS engine into a different vehicle or replacing the fuel rail, double-check that each injector connector is plugged into the harness terminal for the correct cylinder number. The connectors are usually color-coded or labeled, but it's worth verifying against the engine's wiring diagram.

Firing order is the same across all LS variants

Whether you're working with an LS1, LS2, LS3, LS7, or any other LS-family engine, the firing order is always 1-8-4-3-6-5-7-2. The crankshaft design is shared across the family, so the fundamental firing sequence doesn't change. Differences between variants — displacement, compression ratio, valve timing — don't affect the order in which cylinders fire.

This consistency makes LS engines popular for swaps and rebuilds. Once you know the firing order for one LS, you know it for all of them. You won't have to look it up again if you move from an LS1 to an LS3 or vice versa.

What happens if the firing order is wrong

If spark plug wires are connected out of order, the engine will misfire — it will run on some cylinders but not others, or it will fire cylinders at the wrong time in the combustion cycle. You'll notice a rough idle, loss of power, and often a check engine light. The engine may not start at all if the firing order is severely scrambled.

If fuel injectors are connected incorrectly, the engine may start and idle, but it will run poorly. Cylinders will be lean or rich depending on when they're being fed fuel relative to when they fire. The best way to verify the firing order after an engine swap or rebuild is to check the wiring diagram for your specific engine and harness, then trace each wire or connector back to confirm it matches the cylinder number.

Frequently Asked Questions

Can I change the firing order of an LS engine?

No. The firing order is determined by the crankshaft and camshaft design and cannot be altered without completely redesigning those components. You can only work with the firing order that's built into the engine.

Does the firing order matter if I'm just replacing spark plugs?

Only if you're also replacing spark plug wires. If your LS uses coil-on-plug ignition (which most modern ones do), the coils are already wired correctly by the engine harness. You just remove the old spark plug and install the new one in the same hole.

What's the difference between firing order and cylinder numbering?

Cylinder numbering is the physical location of each cylinder (1 through 8). Firing order is the sequence in which those cylinders ignite. Cylinder 1 is always at the front on the driver's side, but it's not always the first to fire — in an LS, cylinder 1 fires first, but in other engines it might fire second or third.

If I swap an LS engine into a different vehicle, do I need to change anything about the firing order?

No. The LS engine's firing order stays the same regardless of what vehicle it's installed in. You only need to make sure the wiring harness for the LS is connected correctly to the engine — the firing order itself doesn't change.

How do I verify the firing order is correct after an engine rebuild?

Check the wiring diagram for your specific LS variant and engine harness, then trace each spark plug wire or coil pack connector back to the engine to confirm it's connected to the correct cylinder. You can also use a timing light and rotate the engine by hand to watch each cylinder fire in sequence, though this is more involved.