How many times does the spark-plug fire?

Answer 1

Spark plugs fire at the top of the compression stroke. That happens once for every rotation of the crankshaft. So it depends on how many rpms your engine is doing at the time (observable on your tachometer). If your engine is idling at 1000 rpms each of your plugs is firing 1000 times a minute.

The spark plug is fired once every two revolutions of the crankshaft on a 4 cycle engine, so at 1000 rpms the spark plug fires 500 times.

Poprivet is right and I stand corrected. They do fire every other rotation of the crankshaft.

Greetings gentlemen. 'Two Stroke' and "4 Stroke" are confusing misnomers. That is inaccurate, all due respect. Once every 2 rotations, and every one revolution on a two stroke cycle engine..... and there is really no such thing as a 2 cycle or 4 cycle engine. A spark plug fires 30 times a second in a 4 cylinder engine running at 1000 rpm's, 1800 times a minute. On engines with a distributor.

One revolution of the crankshaft is two 'strokes' in what the proper term is a " 4 Stroke Cycle" engine. It is important to differentiate between 'stroke' and 'cycle'. It takes 4 movements, one travel of the piston up is a 'stroke'. One travel down is a 'stroke'. It takes 4 strokes to make a cycle..an often misunderstood concept because people say 2 stroke engine, meaning 2 stroke cycle.

OK. The spark plug fires one time per 2 revolutions of the crankshaft. Again, on engines with a distributor. But in many modern engines, for example the Saturn Vue, Ford Escort, just to name a couple, and many other modern engines with coil packs and no distributor, there is a "waste spark" on dual polarity coils, the crankshaft position sensor sends a signal to the ECU, aka PCM, and "tells" the coil to ignite the spark plug at each TDC of the piston, both times it is at TDC therefore it will ignite the plug at the top of the exhaust stroke, before the piston begins to travel down on the intake stroke. That is your 'waste spark' and doubles the figure because it fires on each turn on the crankshaft. Now, on a two stroke, it fires every time anyway...that is why it's called "two stroke". Two strokes complete a cycle. There are reed valves, and one stroke is up and the other is down.... and every down stroke is a power producing stroke. Every time the piston travels down it is producing power to the crank, the plug ignited by a magneto. ~David