Well, I took it in to the local LPG specialist (UK importers of the system it uses) to get the damn document the insurance people need. But it failed the tests! They showed me the emission results, and they were way, way out of kilter on lpg.
The diagnosis: my 2 injectors are knackered. Fitting new injectors solved the problem. It was overfuelling quite a bit, so it should run better now, and it should also use a lot less gas. Although, they will probably need replacing again in a few years, such is the nature of the beast.
The bad news is the £500 bill. The alternative was to go for a whole new LPG system - a newer one which would use better injectors, run better, etc. But that would have been more than a bag of sand, so I decided against.
Hmm, how do I explain this to Abby?
David.