Timing – it has a couple of different meanings when applied to your car’s engine. One of the most critical is ignition timing (not to be confused with engine timing). Ignition timing refers to when spark is created during the engine’s cycle. It needs to be just right or you end up losing power, increasing fuel consumption and producing more emissions in your exhaust.

What’s timing all about?

Your engine runs on a controlled series of explosions. Spark plugs create their spark to ignite fuel vapors. This creates combustion. The explosion then pushes down the piston, which turns the camshaft. However, the plug can’t fire at just any time. It needs to be timed correctly with the engine’s motion.

There are four cycles in an automotive engine (thus the name four stroke). These are:

  • Intake
  • Compression
  • Combustion
  • Exhaust

The spark plug must fire at the right point in these cycles to maximize the power created by combustion. The system should fire before the piston hits top dead center (TDC). The increase in pressure from combustion pushes the piston back down (after reaching TDC), and turns the camshaft. The reason that the plugs need to fire before the piston hits TDC is that if it didn’t happen then, by the time combustion actually occurred, the piston would be so far into its downward motion that the force of the combustion would be largely wasted.

Remember: while gas is highly combustible, it doesn’t burn instantaneously. There is always a delay. By firing before the piston hits TDC, your engine is able to account for this delay and maximize the amount of power each time.

This article originally appeared on YourMechanic.com as What Does Ignition Timing Mean? and was authored by Valerie Johnston.

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