After replacing my valve cover, I went for a test drive, not realizing I had mistakenly left both primary O2s unplugged. Car felt normal and did not show a Service Engine Light. I made a couple light pulls in 2nd gear, had no issues, so I tried 3rd gear and this pull killed the motor. Huge dump of smoke out the exhaust.

For some reason, even though codes were triggered for both O2 sensors, there was no check engine light and no limp mode.