Ignition Question

Hello Forum,

This might be a redundant question? But I haven’t been able to get it straight in my head. I have two questions

(1) On one 360 degree rotation of the crankshaft, how many ignition pulses are there?

(2) Do both coils fire to all 4 plugs with one 360 degree turn of the crank?

Thanks, Spencer

For reference, in each cylinder ---




Pistons in cylinders #1 and #4 rise and fall together.
Pistons in cylinders #2 and #3 rise and fall together.
When 1-4 are at top, 2-3 are at bottom.

When pistons 1-4 are both at top, one is on power stroke, and the other is on exhaust stroke.
The dual wire coil fires once with each crankshaft revolution, at which time it sparks both cylinders 1 and 4.

Whichever 1 or 4 that needs the spark will then combust (compression stroke)
Whichever 1 or 4 that doesn't need the spark (exhaust stroke) gets the spark anyway (wasted spark).

Same thing is happening with the other coil on cylinders #2 and #3.

This design allows the two coils to spark 4 cylinders.

Good Fortune!

4TheKZ1000 wrote: Hello Forum,

This might be a redundant question? But I haven’t been able to get it straight in my head. I have two questions

(1) On one 360 degree rotation of the crankshaft, how many ignition pulses are there?

(2) Do both coils fire to all 4 plugs with one 360 degree turn of the crank?

Thanks, Spencer

In one 360 degree rotation of the crankshaft all 4 plugs fire, but in pairs so there are 2 "pulses." Here's an easy way to look at it - think of the ignition points. The points cam is located on the end of the crankshaft, so for each 360* of crankshaft rotation the points cam also rotates 360*. As it does, it opens each of the 2 sets of ignition points, so in one rotation both sets of points is opened. As each set of points opens it fires its respective coil which in turn causes both spark plugs to which it is attached to fire. So for each crankshaft revolution, all 4 plugs fire, but since as Patton points out no 2 cylinders are on the compression stroke at the same time each time a pair of spark plugs fire only one of their respective cylinders starts its power stroke. As a result, it takes 2 complete revolutions of the crankshaft to fire all 4 cylinders. Ed