It really needs a mechanic with diagnostic equipment to trace the problem, but it sounds like the whole system is shutting down. I would suspect that it could be a fault with the computer.

Ford has been using cooler pipes that make it difficult to break into to fit an external cooler, but there's always a way around a problem. Take your car to AW Automatics in Ferntree Gully and have Andrew take a look at it.

Three years is a very long time to put up with a problem like this, which is very dangerous, as you say. The Parnell system is a well-known one that has been widely used over the years, so there shouldn't be any problem with that. It would be worth checking the water flow to the converter, which can "freeze" up if there isn't sufficient hot water flowing through it, but I would also question the competence of the Ford dealer if they couldn't fix a problem like this in three years. You could also phone Parnell LP Gas Systems directly (03 9315 1699) and enlist their assistance. I am sure they would be happy to help get your car running the way it should.