In some cases a very unstable boardnet voltage can cause misfires. The 123ignition is protected against high voltage peaks and goes in protection mode for a split second when a spike is detected. Most of the time this error occurs when the car battery is charged full again and the voltage regulator starts to work. This problem can be caused by a broken alternator / dynamo or bad voltage regulator. Unfortunately this is impossible to measure with just a standard voltage meter because we talk about high voltage spikes of micro seconds. You could easily test this to drive a while without working alternator / dynamo. Use a fully charged car battery and make sure no other important systems are driven by the dynamo belt, like the coolant pump!!!