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Is the compression good and no clogged cats?
Some more ideas.
Have you checked the cam timing?
The LTFT and the pinging says to me the valve timing is wrong on bank 2.
And what cats did you fit?
That's all very good info, and looks like you know enough to nut your problem out .
Great when we can be on the same page.
Yes you may be correct with varnish buildup on the B2 injectors, since your additive has made a difference.
As an experiment, I would swap all the injectors from B2 to B1, and then see if the B1 trims go high like B2 is doing now.
Is double work, but you'll know.
If the trims do swap over, then have the injectors ultrasonically cleaned.
Did you fit the factory recommended spark plug and gapped correctly?
Here is some info about spark plug function when not firing:
I would think that the 13.9 ohms versus 13.1 ohms would make the injector a fraction lazy, which then has the closed loop correction adding fuel (+ fuel trims), strange that all 3 on one bank read higher than the other bank.
I would still swap them bank to bank for another test.
So other than your P1340, does it now run ok, and have the fuel trims evened out as yet, or are you now willing to swap the injectors bank to bank?