The five-speed automatic in your Calais is a bit of an odd one, Mark, as it was only used for a handful of years and only in the high-feature 3.6-litre V6. Holden switched the car to a six-speed automatic in September 2009, so technically, that would be possible to fit to your car. As with a lot of these things, however, it’s not as simple as finding a gearbox and bolting it in. Modern engineering dictates that the five-speed and six-speed transmissions, while physically similar, may have featured bigger differences in terms of the information they fed to the car’s on-board computer and the program within that computer that, in turn, told the gearbox what to do next.

At the very least, you’d need the electronic transmission-control module to make the six-speed work and possibly some changes to sensors and wiring. Even then, you might find that your speedometer needs recalibration. Unlike the good old days when the transmission was simply a set of gears, a modern transmission these days is a much more sophisticated piece of equipment and does a much more complex job.

I believe Orbital supplies the HSV system and I can't think of any reason that you couldn't fit an Orbital system to your car. It would have to be tuned differently, of course, because your engine is different to the HSV one. There are other liquid-injection systems available, as well as some very well developed vapour-injection systems. One you could check out is the Impco system. The beauty of injection systems is that you can tune them to produce the same performance on LPG and on petrol. Without being exact you could expect to recover the cost of installing a system in around 18 months.

THANKS Ross. We have received a lot of suggestions on what might be causing the battery to go flat. Yours seems to be a plausible explanation and might give our reader a clue on where to look next.