Engine Firing Order | 1-8-4-3-6-5-7-2 | GM, Ford, Mopar & More
When it comes right down to it, the main purpose of every internal combustion engine is to light off that spark. Making sure the air/fuel mixture lights off in order to push the piston down and spin the crankshaft is the number one priority. We understand everything that comes before or after that point is important, too. But if you don’t have that spark in the right spot and at the right time nothing else matters.
One issue that plagues many people when working on an engine is literally getting their plug wires crossed between the distributor cap and the spark plugs (you coil on plug/coil near plug owners don’t have to worry about this). Everything looks fine, but the engine runs rough and won’t accelerate. After hours spent in frustration trying to find the source of the problem, it turns out to be as simple as a couple of plug wires routed to the wrong spark plugs.
What is Firing Order and Why Does it Matter?
An engine can’t just fire its cylinders from front to back for simplicity’s sake. Every time one of the spark plugs fires off in the combustion chamber full of air and fuel mixture, a reaction is started that rapidly develops extreme pressures in the chamber. This expanding pressure presses down on the piston and connecting rod. All these pulses make their way to the crankshaft, and they aren’t gentle.
To protect the health and longevity of an engine, the firing pulses must be balanced from bank-to-bank and from front-to-back. Engine designers try to avoid firing adjacent cylinders consecutively whenever possible. Properly balancing the pulses from compression not only helps protect the crankshaft, but it also results in the engine running more smoothly and produces a better overall exhaust note. Without balanced firing pulses, the engine would run rough, wear unevenly, or even fail catastrophically. Firing order also impacts:
- Power Output: Ensures even power delivery.
- Exhaust Note: Affects the "heartbeat" sound of the engine.
- Efficiency: Improves RPM stability and fuel economy.
Firing Orders Explained
One of the most beautiful things about the V8 engine design is it balances well in a four-stroke firing pattern. Because each cylinder only sees a compression and power stroke every second rotation of the crankshaft (The other rotation is exhaust and intake), that means it requires two full revolutions of the crank for all eight cylinders to fire. But that also slots nicely into 90 degrees of rotation between each firing. 720 degrees divided by 8 cylinders=90.
Why is the number 90 important? Because a cross plane crankshaft, which 99 percent of V8 engines use, positions the rod journals in four quadrants, or every 90 degrees. Typically, the first and last crank journals are in alignment (up and down) while the center two are also paired together (side-to-side). Regardless, it all matches up nicely.
Now, engineers can choose a firing order that spreads the pulses around the engine so that it both runs smoothly and protects the crankshaft. There is no single perfect firing order, although the firing orders for many different engines are quite similar.
GM V8 Firing Order
Most GM engines all have the same firing order. It just makes sense. Not only is the firing order they chose good for both power and engine durability, but a common firing order can make sharing a few common components easier. Need proof? Check out this list:
Chevy V8 Firing Order | 1-8-4-3-6-5-7-2
- Chevrolet Small Block Firing Order: 1-8-4-3-6-5-7-2
- Chevrolet Big Block Firing Order: 1-8-4-3-6-5-7-2
Because of the popularity and longevity of Chevrolet V8 engines, the 1-8-4-3-6-5-7-2 firing order is the one almost every gearhead learns first. These engines came with distributors that spin clockwise, so that’s also a useful reference. As we continue with this discussion, you might be surprised to find how many other engines follow the same design. This includes other engines in the GM family that are no longer produced:
- Oldsmobile V8 Firing Order: 1-8-4-3-6-5-7-2
- Pontiac V8 Firing Order: 1-8-4-3-6-5-7-2
Vortec & LS Engine Firing Order | 1-8-7-2-6-5-4-3
When the LS engine came along, the engineering staff famously swapped the 4 and 7 and the 2 and 3 cylinders in the firing order. This also includes the lineup of iron-block truck engines, especially the 5.3 LS and 4.8 liter engines. They share almost all LS components, so most horsepower enthusiasts consider them in the LSX family of engines, but GM named them “Vortec” for differentiation. LS is branded for performance and Vortec for light duty pickups.
The introduction of distributorless ignition systems in Chevy’s LS series engines brought a significant change: a 1-8-7-2-6-5-4-3 firing order. The swap of cylinders 4 and 7, along with 2 and 3, reduces internal harmonics, improving high-RPM performance and durability.
- LS V8 Firing Order: 1-8-7-2-6-5-4-3
Ford V8 Firing Order
Ford takes an entirely different route. The number one cylinder is the furthest forward on the passenger side (instead of driver) and runs down the passenger bank of cylinders first before moving over to the driver’s side. So, the cylinders start numbering on the passenger side 1-4, then switch over to the driver’s side and run 5-8. Once you understand the difference, it’s no big deal. Just make sure you don’t get mixed up when working on different engines. With a different numbering system, the firing order itself is different too.
The most popular firing order used by Ford is 1-5-4-2-6-3-7-8 in most small block Fords (260/289/302), FE big blocks, and 429/460 big blocks. The 351 Windsor, Cleveland and 351M and 400 engines (and Ford Modular V8s) use 1-3-7-2-6-5-4-8 (watch for the 302 HO/5.0L HO that uses the Windsor firing order due to the camshaft spec’d for these engines), while others like the Flathead Ford firing order use 1-5-4-8-6-3-7-2 (same as Ford’s classic Y-block, the only Ford engine with the distributor in the rear like a SBC).
Mopar Firing Order | 1-8-4-3-6-5-7-2
Mopar V8 engines, from the Small Block Mopar (SBM) to the Big Block Mopar (BBM) and HEMI families, adhere to the 1-8-4-3-6-5-7-2 firing order. However, distributor rotation can vary:
- Small Block Mopar Distributor Rotation: Clockwise
- Big Block Mopar Distributor Rotation: Counterclockwise
- Gen I HEMI Distributor Rotation: Clockwise
- Gen II HEMI Distributor Rotation: Counterclockwise
- Gen III HEMI Distributor Rotation: NA (distributorless system with coil on plug ignition)
AMC Firing Order
The old American Motors Company was the great upstart of automobile manufacturers back in their day. They were always trying to do more with less, especially when it came to budget. Engines are incredibly expensive to design and manufacture from scratch, so one of their tricks was simply to purchase engines for their vehicles from other manufacturers. The list includes the famous Pontiac “Iron Duke” four cylinder, a Buick V6 for Jeep CJ’s, and even Packard V8’s. So, it only makes sense that they would utilize the same numbering system and firing order as GM and Mopar when they introduced their own V8 design all the way back in 1956.
Firing Order Chart
Listed here are all common V8 and inline-six cylinder engine firing orders for you to quickly find and confirm the firing order for the engine you are working on. While you may have memorized the firing order of your favorite engine, having this handy chart around will no doubt help when you’re working on less familiar engines.
What Happens if Firing Order is Wrong & How to Fix It
Once an engine is built and running, firing order issues most often seem to crop up when someone is doing maintenance or some type of repair and pulls the plug wires without paying enough attention to where they came from. Then they get reinstalled in the incorrect order and the next thing you know; you’ve got a misfire.
Symptoms of an incorrect firing order include:
- Engine turns over but won’t start
- Rough running or loud misfires
- Loss of power or stalling
How to Troubleshoot:
- Verify the firing order against the manufacturer’s specs
- Use numbered spark plug wire markers for accuracy
- Test cylinder firing with an infrared thermometer
The solution is as simple as to make sure your plug wires are always properly labeled. And never remove the wires off the distributor unless absolutely necessary. Just in case, use a sharpie to mark the number one terminal on your distributor. And a simple plug wire marker kit is a more reliable way to permanently label plug wires in a clear, easy-to-read way than a marker.
If you do get a couple of wires crossed and you’re trying to figure out which ones are in the wrong place, start by looking up your engine in the firing-order table above to find the correct firing order and distributor rotation. If, for some reason, you’re still having trouble, a simple solution is to use a mini laser thermometer to find the cylinders that aren’t firing. With the engine running, use the thermometer to read the temperature on the exhaust close to the cylinder head. Cylinders that are firing correctly will heat up at approximately the same rate while cylinders that are misfiring will stay relatively colder.
If you find two bad cylinders, try swapping out the plug wires. If you’re still running an older ignition system sometimes a set of good spark plug wires will do the trick! Of course, there’s no guarantee this will be the cure every time, but it’s always a good idea to start with the simplest fixes first. Good luck!
