What the LS firing order is and why it matters

The LS firing order is 1-8-7-2-6-5-4-3, meaning the spark plugs ignite in that sequence as the engine rotates. This order is the same across all LS-family engines — the LS1, LS2, LS3, LS6, LS7, LS9, and their variants. The firing order determines which cylinder fires next, and getting it wrong during spark plug wire installation, ignition coil setup, or engine rebuild will cause the engine to misfire, run rough, or not start at all.

The LS engine uses a distributor-less ignition system in most applications, meaning each coil pack fires one cylinder directly rather than a single distributor sending spark to all eight. This makes the firing order critical when you're replacing coils, spark plugs, or wiring, because you have to match each coil to the correct cylinder position and firing sequence.

Key Takeaways

  • LS firing order is 1-8-7-2-6-5-4-3, and this sequence is identical across all LS engine variants.
  • Cylinder numbering on LS engines runs 1-2-3-4 on the driver's side and 5-6-7-8 on the passenger side, both front to back.
  • Each ignition coil pack connects to one specific cylinder, and swapping coil positions will cause misfires and rough running.
  • Spark plug wires must follow the firing order if your LS uses a traditional distributor setup, which is rare but still found in some older conversions.

LS cylinder numbering: driver's side versus passenger side

LS engines number cylinders in two banks. The driver's side (left bank) holds cylinders 1, 2, 3, and 4, numbered front to back. The passenger side (right bank) holds cylinders 5, 6, 7, and 8, also numbered front to back. This layout is the same whether you're looking at the engine in a Corvette, Camaro, truck, or a custom engine bay in a swap.

When you stand in front of the engine looking at it, cylinder 1 is at the front on the driver's side. Cylinder 8 is at the back on the passenger side. This matters because when you're installing coil packs or replacing spark plugs, you need to know which physical cylinder you're working on so you can connect it to the right coil or wire.

How coil packs connect to the firing order

Most LS engines use eight individual coil packs, one mounted directly over each spark plug. Each coil pack is labeled or positioned to correspond to a cylinder number. The engine computer sends a signal to each coil in the firing order sequence — 1, then 8, then 7, then 2, and so on — telling it when to fire.

If you remove a coil pack and reinstall it on the wrong cylinder, the engine will misfire on that cylinder because the spark will arrive at the wrong time in the combustion cycle. The engine may start and idle, but it will run rough, throw a misfire code, and lose power. Always photograph or label coil positions before you remove them, or consult your engine's wiring diagram to confirm which coil goes where.

Some aftermarket or older LS setups use a traditional distributor with plug wires instead of coil packs. In those cases, the wires must be routed to the distributor cap in firing order sequence, and the distributor rotor must point to cylinder 1 when the engine is at top dead center on the number 1 cylinder.

Spark plug wire routing for distributor-based LS setups

If you're running an LS engine with a distributor and spark plug wires — common in engine swaps or older conversions — the wires must follow the firing order around the distributor cap. Starting from the terminal where the rotor points at top dead center (cylinder 1), you route wires in order: 1-8-7-2-6-5-4-3, going around the cap.

The rotor inside the distributor spins and points to each terminal in sequence as the engine turns. When the rotor points to the terminal for cylinder 1, the ignition fires cylinder 1. A quarter turn later, it points to cylinder 8, and so on. If the wires are out of order, the spark reaches the wrong cylinder at the wrong time, and the engine will not run.

To confirm you have the wires in the right order, locate the number 1 terminal on the distributor cap (usually marked or indicated in the cap's design), then trace each wire back to its cylinder. The cap should show cylinder numbers, or you can reference your engine's service manual.

Setting top dead center and confirming cylinder 1

Before you install coils, wires, or a distributor, you need to know where cylinder 1 is at top dead center (TDC) — the point where the piston in cylinder 1 reaches the top of its stroke and is ready to fire. At TDC, both the intake and exhaust valves for cylinder 1 are closed, and the spark plug is about to ignite the fuel mixture.

To find TDC on an LS engine, remove the valve cover on the driver's side and locate the intake and exhaust rocker arms for cylinder 1 (the front pair). Rotate the engine by hand using a socket on the crankshaft bolt until both rocker arms are loose and the piston is rising. Continue rotating slowly until the timing mark on the crankshaft pulley aligns with the zero mark on the timing cover. At this point, cylinder 1 is at TDC, and you can install the distributor rotor or confirm coil pack positions.

Common mistakes when installing or replacing ignition components

The most frequent error is installing coil packs in the wrong order after removing them for spark plug replacement or cleaning. Even if you only remove two or three coils, photograph their positions or label them before you take them off. A single coil in the wrong spot will cause a misfire code and rough running.

Another common mistake is assuming that because the LS is a modern engine, the firing order is the same as a small-block Chevy (which fires 1-8-4-3-6-5-7-2). It is not. The LS firing order is different, and using a small-block distributor or wiring diagram on an LS engine will result in a no-start or severe misfire.

If you are swapping an LS engine into a vehicle and using a traditional distributor instead of coil packs, verify that the distributor is designed for LS engines and that the cap terminals are labeled correctly. Some universal distributors require you to drill and mark the cap yourself, and mistakes here are straightforward to make and hard to spot until you try to start the engine.

Frequently Asked Questions

What is the LS firing order again?

The LS firing order is 1-8-7-2-6-5-4-3. This sequence is the same for all LS engines, including the LS1, LS2, LS3, LS6, LS7, and LS9. The number refers to which cylinder fires next as the engine rotates.

Can I use a small-block Chevy distributor on an LS engine?

No. A small-block Chevy fires in a different order (1-8-4-3-6-5-7-2) and has a different distributor cap layout. Using a small-block distributor on an LS will cause misfires or a no-start. You need a distributor designed specifically for LS engines or a coil-pack ignition system.

What happens if I put a coil pack on the wrong cylinder?

The engine will misfire on that cylinder because the spark will fire at the wrong time in the combustion cycle. You will see a misfire code for that cylinder, the engine will run rough, and you may lose power. Swap the coil back to the correct cylinder to fix it.

Do all LS engines use coil packs, or do some use distributors?

Factory LS engines use coil packs. Distributors are found mainly in engine swaps or custom builds where the builder chose a traditional ignition system. If you are working on a stock LS, you are almost certainly dealing with coil packs, not a distributor.

How do I know which cylinder is number 1 on my LS engine?

Cylinder 1 is the front cylinder on the driver's side (left bank). Cylinders 1-2-3-4 run front to back on the driver's side, and cylinders 5-6-7-8 run front to back on the passenger side. If you are unsure, consult your engine's service manual or wiring diagram.