When the Auto logic was connected did he have a look at the serial data ie Fuel trim per bank, Coolant temp sensor, injection duration, ect.
I think a lot of people grab themselves a bit of diagnostic kit, plug it in and expect to get the magic answer in the way of a fault code. The data will paint a very accurate picture of the way the engine is running.
It could be a coolant temp sensor that is reading a very low temp and is causing an over fuel situation,
a lazy lambda on one bank,
a failing coil that again is causing over fuel
a TPS that is showing part throttle reading on idle,
a partially blocked cat that is choking the engine on one bank.
With all the plugs out of the engine, keep them in the original order. What state are they in.
The ones from the bank you suspect as failed, are they black and ones from the good bank, brown.The end of a spark plug will tell you a lot about how the cylinder is running.
If a lambda sensor has gone down, the corresponding bank will over fuel. Once all the plugs are fouled on that bank you had it.
Let me know what state they are in. There is a simple way to test the lambda sensor with a voltmeter and you can see how that bank is fueling.