Firing Order And Firing Interval: 7 Facts You Should Know

Firing order and firing interval have different meanings.

Firing order is the sequence in which the cylinders inside a multi cylinder engine are fired whereas firing interval is the time duration after which the same spark plug (cylinder) gets fired. Firing interval can be used in a single cylinder engine as well whereas firing order exists only when there are multiple cylinders used.

What is firing order?

Firing order helps reducing the chances of vibrations and regulates proper heat transfer.

As discussed in above section, firing order is the sequence with which cylinders inside the engine are fired. This term comes into play when there are multiple cylinders inside an engine.

Firing order of multi cylinder engines

Firing order means the chronology with which the cylinders are fired.

Below are some of the common firing orders used for different types of multi cylinder engine-

Number of cylindersFiring orderEngines using respective firing order
21-2Buick Model B
31-3-2Perodua Kancil engine
41-3-4-2,1-2-4-3Ford Taunus, Ford Kent
51-2-4-5-3,
1-3-5-4-2
Volvo 850, GM Atlas Engine
61-5-3-6-2-4,
1-4-3-6-2-5
Nissan L engine, Volkswagen V6s
71-3-5-7-2-4-6Radial engine
81-8-7-3-6-5-4-2,
1-8-7-2-6-5-4-3
Nissan VK engine, GM LS engine
91-10-9-4-3-6-5-8-7,
1-6-5-10-2-7-3-8-4-9
Dodge Viper V10, BMW S85, Ford V10
Table: Firing orders of multi cylinder engines with examples
Firing order and firing interval
Image: Numbering of cylinders in multi cylinder engine

Image credits: Wikipedia

What is firing interval?

Firing interval is the time between two successive firings of same cylinder/spark plug.

The spark plug has to fire during the ignition stroke. Firing of the spark plug is so precisely timed that it automatically fires when its the time for ignition stroke. If it takes x milliseconds to complete one full cycle then after every x milliseconds, firing takes place.

What is the significance of firing interval?

Anything which is more systematic and more even works more efficiently.

The significance of firing interval is as follows-

  • Minimizes vibrations.
  • Provides increased number of even pressure pulses.
  • Uneven firing interval causes throaty and growly sound in engines

What happens if firing order is not maintained?

The cylinders are fired in a particular sequence because of vibrations and heat transfer issues.

If the firing order is not maintained, lets say, if adjacent cylinders keep firing for a long time. Then the heat generated inside the engine will be very high and high sink temperature is always less efficient. The vibrations from the adjacent cylinders will have serious impact on bearings supporting the crankshaft.

Hence, a proper firing order is desirable.

How is firing order controlled/set?

The firing order is controlled by the ignition system of the engine. It provides necessary current to specific cylinders at specific times when ignition is required.

The distributor controls the spark in each spark plug of a multi cylinder engine in correct order. Changing the distributor position will directly affect the firing order of the engine. But this work needs to be done by expert mechanic. Changing of firing order is not recommended.

How is firing interval controlled/set?

The ignition system of the engine also controls the firing interval. It gives the spark at exact moment when required.

Firing interval is controlled by the action of cam which acts as circuit breaker. When the circuit breaker is open, capacitor starts charging creating a high voltage surge in the circuit. This high voltage surge creates the spark. The cam rotation is perfectly timed in a manner such that it breaks the circuit at the precise moment.  

Different parts used in controlling firing order and firing interval

The ignition system of the vehicle controls the firing order and firing interval of the engine. Most commonly used ignition system is magneto and battery ignition system.

In a magneto ignition system, following parts are used-

  • Magneto– A rotating magnet that controls the voltage.
  • Distributor– It distributes the current to the spark plugs in a correct sequence.
  • Capacitor– Capacitor are nothing two parallel metal plates whose each end is connected to circuit. It is used for storing charge
  • Spark plugs– Spark plugs are responsible for igniting the air fuel mixture.

Magneto itself generates power for the ignition system. Hence, it does not need any external source of power. In battery ignition system, batteries are used as external power source.