Ok so got everything back together
new Fuel filter/ PCV / new VVT solenoids / swapped ignition modules- coils and injectors cleaned / new spark plugs.
engine idles smooth and has great performance until
misfires- p030 2 / 4/ /6 /8 - p0300 and P0430 catalyst below threshold.
Nothing makes sense
car will drive without issue/ smooth idle when cold and once warm up then drive 30 miles when at 65-70mph hit throttle up 110-120 and get a slight pinging noise pre ignition -
car cruises at 120 mph fine slow back to 70 mph hit cruise for 15 miles all is fine no code - o2 sensors look fine (.70 - .10)
hit the gas pinging again then a slight shudder and low performance mode P0430 flagged pending
slow to 50 MPH then hit accelerator back to 75 MPH and pinging followed by misfires p0302 / 304 / 306 / 308 / 300.
This is all within 50 miles distance check engine MIL sets.
any ideas???

Just to add the engine before doing injectors had mis fire codes on all cylinders
replaced VVT Solenoid on both sides is it possible I got a bad or faulty VVT solenoid replacement part on the driver aide since its just that side throwing misfire codes?

After all that, did you swap coils/plugs from 1 side to the other?

What is your fuel pressure? Fuel trims? Correct spark plug gap?

Fuel Pressure is 54.8 PSI / Spark plug gap - plugs were NGK pre-gap - good point I was wondering about the gap, but the plugs are the same as 1,3,5,7 without issues.
Yes - moved coils between sides and issue stayed with the cylinder - its only has misfire on 2,4,6,8
I thought Fuel Pressure should be closer to 58 PSI, I also cleaned the injectors which were not working well on 2.4.6.8 and getting bad on 1,3,5,7, so ALL injectors sonic washed cleaned and tested.
new fuel filter as well.

Are you able to check the MAF flow rate for both sensors? Are you getting excessive lean/rich fuel trims?

P0430 is typically a symptom of misfires, not the cause. However, I have read online some suggest that a clogged/damaged catalytic converter may cause misfires. I don't know if this is the case.

If you don't trust your fuel trims when the engine is hot, try swapping the O2 sensors from 1 side to the other and see if the misfires move.

Other than that, I'm at a loss. Goodluck.

Appreciate it - yeah I am down to pulling right side valve cover and doing a close inspection of the valve timing.
The last 2 trips there is no longer a P0430 just misfires under a heavy load / acceleration.
I was hoping for sensors, ignition coil module, spark plugs, anything but having the get into the timing mechanisms as these are tedious, and if off a little bit engine will not run right or worse valve hits piston and engine is done.
going to meticulously look at everything - blow out oil passages look for anything blocked or restricted this car sat a long time so is possible a small patch of gooey oil is still in there
wish me luck...

The left front VVT solenoid I replaced a couple weeks ago does not seem to be opening far enough and its not staying open.
The original one is loose and slaps around not tight.
witing on the next new VVT Solenoid to check operation - this is definitely a problem area.
the chain tensioners were oul filled and locked inplace until VVT Solenoid removed then move a small amount seem very tight.
difficult to really test VVT but it looks clean by appearances but not sure how to test that.
cam lobes are all in good shape.

Alright -
After fuel injector cleaning / replacing all but 1 coil on cylinder 6 we are still getting misfires on 2,4,6,8
fuel trims: what would be an acceptable fuel trim between bank 1 and 2 sensor 1 and 2
The intake vacuum is 11.4 mhg at idle and 14 - 16 mhg while driving
I am now at a total loss :
Fuel trims are even, fuel rail pressure is between 53 PSI and 56 PSI have seen spikes to 58 PSI while driving
When cold there is definitely a miss on the left side once it warms up its very smooth - acceleration is Smooth up to 75 MPH steady pull no hesitation and once it gets to 4500 rpm engine pings a bit then flutters, then low performance mode, and PIDs P0302 /304/306/308 0300 random misfires only on left side the 2,4,6,8 misfires
Checked Plug, and coils - unless there might be a broken wire somewhere I have not done any electrical tests because it works in lower performance.
Fuel regulator seems to be doing its job ...
I put a stiff piece of paper on the exhaust and notice the paper sucks back like a popping - shouldn't there be a steady exhaust pressure and not a suction back?

sounds like you have a valve train problem on the problem bank....could be sludge as you suggest....have you tried a crankcase/oil passage cleaner....maybe one that you run for 10 minutes or so and drain and refill....the sucking you mention at the exhaust is definitely a valve train issue....exhaust valve open a little on intake stroke...maybe a compression check if not already done

Well after looking at everything the only thing that makes sense with what is happening:
https://motorsrun.com/burnt-valve/
Sticking valves or burned valve - may need to have a compression test done to see what that reveals.
is it possible to just pull plugs and turn engine over without damaging anything on these XKRs suspect there is a procedure to do a compression check

Just pull the plugs and disable the fuel system and you can do the comp test. The car has been running so if anything in the valve train is wonky it has already happened. There is also a cylinder leakdown test that isoltes the valves even better

Check the manual for compression test procedure. It will tell you how to interpret the results also.

Engine should also be warm before the procedure.

At this point the owner just wants to get rid of the car.
its NOT making any weird noises just low performance and misfires.

Going to just call some folks or take it to an auction. It is located in Dripping Springs PM if interested...

Resurrecting this fantastic thread for two reasons. Firstly, to thank gkubrak for the useful information, both here and via PM, without which I would not have been confident enough to attempt this job. My valley hose burst last weekend and the car was recovered home. I am in the same position whereby the EGR bolts are made of chocolate and there was no way it was coming off, rendering the TB elbow un-removable. Today I managed to move it out of the way enough to get to the rear supercharger bolt and subsequently pull the elbow out through the hole where the supercharger used to be. It's now all laid out on the bench ready for me to clean, inspect, probably replace bearings etc..

The second reason is to try and get some help along the way. I took plenty of photos before and during the work to remove everything so I should be able to get it all back together, however I found one pipe had popped off and I can't see where it should go. Can anyone identify the pipe with the blue arrow in this photo? The other pipe attached is the vacuum pipe from the multiple T-connectors originating from the supercharger outlet, but this pipe disappears underneath. It's only about 8 inches long so it can't go far...

Its part of the secondary air injection system, which most of us in the USA don't have... You might want to look it up in the manual. Probably goes to the unit itself at the front of the car.

Thank you, gkubrak. Sure enough the tube appears to go to this thing which I don't think I've ever seen before. At least, I've not paid it any attention. The pipe would not stay on there due to the fact it's aged and gone hard so I've since replaced it with a new piece of silicone pipe.



I managed to replace the valley hoses today with silicone ones from Swallows Racing. £80 for the pair which I thought was pretty reasonable. I also removed the EGR with the elbow on the bench and have bought some M6 x 55 stainless steel hex bolts to replace the dreadful torx ones for when it goes back in. I'm now waiting on the pile of gaskets and the supercharger snout to be returned from having the bearings and pulley replaced before I start putting it back together.

You have to be careful using some types of silicone for vacuum lines, they tend to collapse and prevent flow when they get warm.

Thanks, Cee Jay. I opted for silicone hose which specified vacuum as an application, it's quite thick walled. I shall check all the lines when I next run it up to temperature just to be sure though.