Filter is a good call, I have an OK one you can have but not much good if you can't get to CF. Could be an electrical glitch tripping the lpg system out or a genuine leak. Bubbly water in a spray can is good for leak checking. Ignition parts need to be good too but I think you'd diagnose problems there pretty easily.
I have some lpg software and connectors that might help but again only really at CF cost I'm flat out and away from home until Thursday night.
If any help to your despair I getting rid of the log from my xj and you're welcome to any part or all of it. It's OMVL not prins but good kit.