The switch is a simple push button to toggle between LPG and petrol. In normal operation the red (bottom left) and green (bottom right) LEDs will flash, indicating that the engine is running on petrol until it has warmed up - usually about 4 minutes. Once it's warmed up, the red LED goes green and some of the four LEDs in the right-hand column will light to indicate approximately how much LPG is left in the tank.
The tank replaces the spare wheel and, because it's taller than the wheel, foam rubber is used to raise the boot floor by about two inches (50mm).
The conversion was carried out by P & T Autogas in Macclesfield. They had the car for one week. It runs well (sometimes - see below) and I have no complaints about the work. It does about 4 miles per litre of LPG around town. This may seem poor but it equates to about 18mpg and the car often does less than 24mpg on petrol. If you consider that LPG is currently half the cost of unleaded petrol, it's actually more economical to run on LPG. I anticipate getting better mpg on a long run. Curiously, the MPG computer still gives plausible readings for instantaneous and average. I don't understand how this is possible! I thought that the petrol simply circulates at normal pump pressure. Maybe the ECU is basing its calculation on injector opening times, rather than using a flow meter?
The car has always had a slight misfire when cruising at 47 mph. This is much worse on LPG and stretches from 40 - 55mph. I've replaced plugs, leads, coil pack and cam position sensor (which came up in the error test) without fixing it.
In addition, the car runs smoothly on LPG only some of the time. The rest of the time it is reluctant to tickover smoothly or accelerate smoothly unless I "kick down", at which point it roars away with much gusto and occasional "popping" from under the bonnet. It appears to run best when the gas tank is no more than half full, which makes me wonder if the regulator is faulty. Investigation continues.
The Vauxhall expert told me that the "E GAS" LPG ECU has only a rich/weak adjustment, whereas other makes have a more comprehensive adjustment capability based on engine speed etc. He told me that it was impossible to get the mixture right at every point in the rev range. P&T refuted this and stated that the car had an inherent fault which was causing the misfire. I have changed the coil pack and plug leads withut making any improvement. Frankly, there isn't much left to replace now so I'm out of ideas!