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So on an old school car, when trying to determine if the noise from the engine is a rod knock? You would pull off the spark plug boot from each cylinder one at a time. If the noise changed (compression with spark event, raising cylinder pressure) when removing the spark on a cylinder STOPS. It's likely a bad rod bearing.

Now that we have COP (coil on plug) you disconnect the connector from the coil pack on each cylinder.
The difference being:
Now that we have OBD 2 systems, if you remove the connector the DME see's your actions and will usually leave that cylinder turned off. We don't want that, so we must take an extra step:

Now we can do the above test with a scanner hooked up:
Start engine, remove connector from #1. Noise still present?
Key On Engine off (KOEO) clear faults. Reconnecting #1, Start car and remove #2.

Keep repeating the above until you find one cylinder that makes the engine quieter.
Bad rod bearing on THAT cylinder. He got to the offending one with #1.

Most usually, the rod bearings that go bad first, are the two farthest back in the engine. Owing to distance from the oil pump/supply.
Thanks for the response! Two things led me to ask my earlier question; 1) what connector are we talking about (never heard of a 'cylinder connector' before) and 2) what could possibly quiet down a bad rod bearing?

Continuing on with the second question; why does that change the sound? I probably just don't know what I'm talking about but I assume the noise comes from the rod scraping/bouncing off of the rough bearing surface... and I don't see why that would change due to lack of spark. The rod is still moving on the bearing with the rotation of the engine, is it not?
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