If you start up from cold on gas, the vaporiser is not being heated by engine coolant. There is a refrigerating effect as the gas within it vapourises. It will freeze up and stick, possibly causing weak mixture backfiring or gas leakage. If you run the engine up to temp. on petrol before switching over to gas this cannot occur as the engine coolant will already be hot. Don't be fooled into thinking that the air is too warm for freezing to occur, outside temperatures do not have to be down to freezing level for this to happen. The vapouriser may freeze at temperatures up to + 25 degrees Centigrade, especially if the air is very damp..

Care for your petrol injectors

To put this into context, here's a little analogy -

After cutting hedges, a wise man will clean and oil his garden shears before he puts them away. They will not rust or lose their edge whilst in the shed. They will be ready for the next use, whenever that may be.

A few cases of partially blocked petrol injectors in dual - fuel vehicles have encouraged us to investigate and find the cause.

The problem seems to occur mostly with larger engined cars that have covered a lot of miles before LPG conversion. Later, after running the car on LPG almost exclusively (as you would!) owners have found that petrol operation has become erratic and in one case the vehicle was practically undrivable on petrol, although it ran perfectly on LPG. Much examination showed that the injectors were blocked to the extent that their spray pattern was seriously affected. A miraculous improvement was afforded by the addition of a good quality injector cleaner to the petrol, followed by a few miles of petrol driving.

It appears that a car that has done a lot of miles (and maybe not had its injectors cleaned as often as it might) will have a 'skin' of carbon deposited on the injector heads. Whilst making no immediate difference when running on petrol (of course, all injectors will eventually become blocked if they are not cleaned) this coating can expand and harden when running the engine on LPG. Leaving your petrol injectors dirty and redundant for long periods is likely to cause problems later.

The problem is by no means sure to occur in any particular type of injector, vehicle or engine and the incidence is quite low (in the order of 1% of converted vehicles) but prevention is always better than cure.

OK, we are lucky enough to have our vehicles converted to run on a much less expensive fuel, but we still rely on petrol as a back - up. We want it to work when we do have to use it. To avoid problems altogether, there is a simple and inexpensive measure you can take right now!

Add an injector cleaner to your next tank of petrol (STP, Wynn's and other good brands are recommended) and your injectors will be cleaned up every time petrol is selected. If you are in the good habit of starting up on petrol and running the engine up to temp. before switching over to LPG, you will be preventing this problem from occurring. If you have an LPG system that will not switch over until a pre-determined temp. has been reached, you won't even have to give it a thought!

Someone suggested that the addition of injector cleaner to petrol is a 'hidden' cost of LPG use, one ignored by the conversion industry........

But injector cleaner is designed for use when running on petrol, LPG conversion or not!

The best way to avoid both of the above problems is to select the petrol only position on the first start of the day. If you do this you will be cleaning your petrol injectors and ensuring that the vaporiser will not freeze up.