L322 4.2SC misfire after engine rebuild

Hi all, looking to tap into the brains trust for thoughts on how to solve the latest challenge…

A brief recap:
1. I’ve owned car for about 10 years Engine has done about 200k, I rebuilt the gearbox but failed MoT due to excessive emissions. Investigations confirmed some exhaust valves leaking. Stripped heads and confirmed all exhaust valves and seats had serious pitting and one was broken.
2. Removed heads, skimmed, valves, guides and seats all done - vsr due to long term running on lpg.
3. Refitted heads, rebuilt supercharger, fitted new timing chains, belts and water pump.
4. Engine started up fine and ran nicely when parked but on test drive serious pinking/knocking and associated power loss.

Thoughts on possible culprits ?

1. Induction leak, running over lean ?
2. Ignition timing disturbed somehow?
3. Engine / cam timing set incorrectly ?

Thanks all

Andy

LPG is the work of the devil... Killed more good engines than a few in my experience.
Any DTC's?
Smoke test the inlet to identify any induction leaks, then do the same for the exhaust, injection & spark timing is by CKP/CMP sensor input to the ECM, did you replace the camshaft dephasers?

You need to be running 100% on petrol before even thinking about lpg

Injector issues or wiring to them. You may have to back over what you have done