Engines are the heart of every vehicle, and different engine types operate in different ways. One of the things that differentiates engines from each other is firing order. If the engine is the heart, the firing order is its heartbeat. But what is firing order exactly, and can you tune it how you like?
In a gasoline engine, the firing order or ignition sequence indicates the order and timing of when its spark plugs fire. In a diesel engine, firing order indicates the sequence of fuel injection.
The crankshaft and camshaft design determine the firing order. The cylinders are arranged so their power strokes fire in the proper succession. The firing order also differs depending on the number of cylinders and the configuration of the engine. Firing order is usually written as a sequence of numbers or a combination of numbers and letters to identify the exact cylinders being triggered.
Firing order is important because of valve timing. The spark plugs need to fire in sequence with the operation of the valves and pistons.
Here are some examples of firing orders:
A V6 Ford will typically be 1-4-2-5-3-6. A V6 Chevy may be 1-6-5-4-3-2 or 1-2-3-4-5-6, which is a very popular firing order for V6 engines. Inline 6-cylinder engines are almost always 1-5-3-6-2-4. Four-cylinder in-line engines tend to favor the 1-3-4-2 firing order.
GM (except for Cadillac) and Chrysler/Plymouth/Dodge V8s for many years had a 1-8-4-3-6-5-7-2 firing order. Newer Chevy engines like the 4.8/5.3/6.0L engines sport a 1-8-7-2-6-5-4-3 firing order.
A V8 Ford would be 1-5-4-2-6-3-7-8 or 1-3-7-2-6-5-4-8 depending on year model and or engine size.
But again, knowing how the cylinders are numbered is just as important as the firing order.
Firing order impacts the engine’s noise, generated power, level of vibration, and even its fuel economy.
Now, you might wonder why the spark plugs or injectors don’t just fire in order, like 1-2-3-4 (and so on). If the cylinders fire in order, it would produce uneven torsional forces on the crankshaft, which may cause it to deform or even break. In addition, because of how much power the firing phase releases, it can stress the engine if the firing occurs simultaneously in adjacent cylinders. To avoid this, manufacturers adjust the ignition sequence to maintain balance in the engine.
Ignition timing changes with engine speed and load to manage cylinder pressure and maximize the power generated during each power stroke.
It’s difficult to talk about firing order without also talking about firing intervals. The firing interval is the amount of time that passes between each cylinder’s ignition following the firing order. The engine’s power strokes usually need to be spaced at equal firing intervals for the engine to run smoothly. These intervals rely on a specific formula based on the number of strokes and the number of cylinders.
Some engines forgo the equal firing intervals entirely though. These engines use uneven firing intervals instead, which affect its smoothness but can be worth the tradeoff for higher performance.
If your engine has a distributor ignition, you’ll often find its firing order cast or stamped onto its intake manifold. You can also find it in your vehicle’s manual. If neither of these yields results, you might want to do a little research to find out your engine’s exact firing order. This is useful for connecting up sparking plug leads properly and connecting test equipment to your ignition system.
Here are some of the most common firing orders found in in-line engines:
| Type of Engine | Common Firing Orders |
| Four-cylinder in-line engines | 1-2-4-3, 1-3-4-2 |
| Six-cylinder in-line engines | If connected pistons are 1-6, 3-4, and 2-5: 1-3-2-6-4-5, 1-3-5-6-4-2, 1-4-5-6-3-2, 1-4-2-6-3-5 If connected pistons are 1-6, 2-5, and 3-4: 1-2-3-6-5-4, 1-2-4-6-5-3, 1-5-4-6-2-3, 1-5-3-6-2-4 |
| Five-cylinder in-line engines | 1-2-4-5-3 |
In the case of v-type engines, here are the common firing orders:
| Type of Engine | Common Firing Orders |
| V6 engines | With an angle of 90 degrees: R1-L2-R2-L3-L1-R3 or R1-L3-R3-L2-R2-L1 |
| With an angle of 60 degrees: R1-L1-R2-L2-R3-L3 | |
| V10 engines | R1-L5-R5-L2-R2-L3-R3-L4-R4-L1, R1-L1-R5-L5-R2-L2-R3-L3-R4-L4 |
V12 and V8 engines tend to use more varied firing orders.
Tuning your engine’s firing order is no easy feat. It requires you to replace the engine’s crankshaft (or at least the camshaft), which often impacts your vehicle’s reliability. However, you can increase your horsepower if you pick the right kind of crankshaft and camshaft and choose the optimum firing order. Whether it’s worth it is entirely up to you.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.