Less sparks on ignition coil

The internal insulation of the coil may be degrading.

To test the integrity of the insulation a Fluke meter with the ability to measure Conductance is needed. Set the meter to conductance and measure from a spark plug wire tower to the electrical plug. In a good coil, the meter will show a number that fluctuates. A bad coil, the meter will show "OL". Check both coil pairs to the electrical connector.

In this type of ignition, the primary and secondary windings of the coil should never interact. When the meter reads "OL" this means that there is some minor interaction because the resistance is low enough.

If you’re testing with a realistic setup of ignition leads and spark plugs then you should see similar sparks on both plugs. If you’re testing under different conditions then it’s quite possible that one side will arc before the other and draw most of the energy from the coil. So if you’re testing under realistic conditions then you likely have a problem, otherwise it may just be to do with the setup when you’re testing.