How does the ECU detect a misfiring cylinder using input from the Crankshaft Position (CKP) sensor?

1. By measuring the increase in alternator output voltage during a cylinder firing stroke
2. By detecting a temporary drop in crankshaft rotational speed (deceleration) during that cylinder's power stroke
3. By measuring the temperature of the exhaust manifold runner using a thermocouple
4. By checking if the ignition switch remains closed during the combustion cycle