I dont do many miles, never use lpg and it causes a coolant leak, so I plan to decommission it.looks as if I need to drain half the coolant, remove the plenum and then the hoses that were drilled into the inlet manifold. Then I need to blank off 8 holes in the inlet manifold and 1 in the plenum?
I assume theres no need to remove the actual manifold itself. I can disconnect the ECU easily enough, and then examine how it was spliced into the engine ecu.... I may leave the tank in place for now, but if so, how should I seal it off (it's empty). Any other key jobs?

No need to drain the coolant, you'll lose a bit but not a lot, just take the Tee's out (assuming it has been plumbed in parallel with the heater) and replace with straight joiners (or replace the complete hoses with new). The spuds into the manifold will be M6 (normally, or they could be M5) thread so all you need are some very short bolts with a dollop of Hylomar on the threads. That will both act as a thread lock and make sure they seal. I run a single point system on mine but drilled my manifold years ago while it was off in case I ever wanted to change for a multipoint and Hylomar coated bolts have sealed the holes for years now.

Wiring might be a bit more complicated. It will probably have a tap into the Brown/Yellow wire that feeds ignition switched power to the fuel injectors, another one from the TPS feed and the injector cut wires. Just occasionally, the installer will also have connected into one of the lambda sensor feeds too but most don't. The feed from the ECU to each petrol injector will have been cut and a pair or wires connected to intercept the pulses from the ECU to each injector (these intercepts will be a colour and the same colour with a black stripe onto each injector feed), so you will need to remove those and reconnect the feed direct from the ECU to the injector.

If you look at the multivalve on the tank, it will have a knurled knob on it somewhere. That is the shut off for the output in addition to the electrically operated solenoid valve, so screwing that in will isolate the output from the tank.

Tnx. Wd 10mm bolt length be about right, do you think? Or shorter...i'll need to order some

10mm will probably be a bit long, they need to be roughly the same as the thickness of the manifold where it is drilled. You don't really want a length of the bolt sticking into the intake obstructing the airflow. Might be a good idea to take one of the spuds out and see if you can gauge the length you need.

Turns out they're 12 mm, perhaps helps with dispersal? But it looks like the thread was only in about 8mm ( the remainder is black)

M12 threads? That's huge!

No, M6, but 12 mm long. Only the first 8mm of thread was clean, so presumably 4mm protrusion for the jet

Ahh that makes sense. So ideally you need 8mm long M6 bolts (or longer ones and cut them down).

Richard, couple of questions: i. Where do i see the knurled knob in the pic above? ii. The lpg ecu is now depowered. I may leave the re-wiring until last...is the ecm to injector wiring connection still continuous via the depowered lpg ecu? Or it won't work until i break and remake the injector wiring ?

Ooh, 4 hole filled toroidal tank. The pipe coming in from the right is the fill line, that has a non-return valve inside the brass bit so you can fill the tank but if you disconnect the pipe to it, gas doesn't come out. Next to that is the level gauge which is pretty self explanatory, the thing with a red cap on it is a pressure relief valve and the bit on the left is the outlet. That has an electrical solenoid valve in it to shut off the gas outlet as soon as the power is taken off. I'm not sure if a 4 hole outlet has a manual shut off or not, if there is a knurled knob on that bit, it does, if there isn't it doesn't but if the solenoid is disconnected then it can't open. If you want to be really belt and braces, you can remove the small nut in the centre of the solenoid coil and lift the coil off, then the outlet can never open.

If you do decide to remove it, let me know as it would go nicely in the boot of the Rioja red 4.0SE I've just bought (and has been claimed as hers by the other half) as not only was the tank in it fitted the wrong way round, the bodger that 'installed' the system only fitted a 70 litre tank so there's a huge gap all the way round it and it will need filling more often. Not so good now LPG is getting harder to find and the maximum range possible is desirable.