Hi all,
2015 RR Sport 5.0 SC.
Posting from Australia, now seeking help globally !

In August I had the timing Chains, Guides, and Tensioners replaced, and Bank2 head rebuilt with new genuine LR lifters/stem seals, seats etc,
Also replaced: Brand new LR spec spark plugs, and 8 new non-genuine injectors. These were not flow tested how ever. They were from an online store, reasonable reviews and were 1/10th the price of genuine LR injectors.
Coilpacks have not been replaced and we are assuming coilpacks are fine, no misfire codes in ECU.

Fast Forward, Got the car back from the shop, and started getting P430 Cat Efficiency below threshold.

With a scan tool, was able to see Bank 2 (left side, passenger side in Aus), Sensor 2 (inside the cat) showing eratic values, 0.2v, 0.3v, 0.8v, 0.75v, 0.233v, 0.35v, and so on.. just jumping around constantly.
Bank 1 (drivers side, right side in Aus) Sensor 2 how ever is fairly stable either at 0.755v when revving or dips down to 0.233v on idle, but its not jumping around.
Also getting no P420 code for Bank 1. so Bank 1 is my reference when comparing anything.

Swapped Bank 1 downstream(sensor2) O2 Sensor with Bank 2. The pinouts/wires are all the same, just the plug harness has a guid-nipple i had to shave off a little with a stanley knife.

Same issue - Bank 2, Cat showing P430.

Unbolted the cat at a friends workshop this weekend, ran Caustic soda through it, and hot soapy water through it, flushed it out, cleaned it up really nice, re-installed,

Same issue. The obd2 scanner how ever is showing higher efficiency levels when i do a Cat test. Before all of this testing it would sit around 20-50% efficiency, minimum value was meant to be 100%, maximum was 165%. For reference: Cat 1 on Bank 1 shows 161% steady all the time. So im using this as a guide.

Now, i do have a misfire somewhere on bank 2.. one of those 4 injectors is misfiring because i can feel the unsteady idle, and subtle pops of air in the exhaust.
I have swapped coil packs around Bank 1 and 2, to rule those out.

More symptoms:

• When cruising at 100km/h on the motorway, if i ease onto the gas and build up rebs, the car vibrates a decent amount until the revs pass around 3000 and then its smooth.
• Slightly rough idle, not really noticeable sometimes, but other times it is.
• Taking off occaionally i get a stutter, and while downshifting

Could the misfire throw off sensor 2 inside the cat ?

Why would it not throw off sensor 1.

Any suggestions or questions would help, Thank you