“Which type of LPG conversion kit should I buy” is one of the most frequent questions that we are asked. The two main decisions about the kit are the type of front-end system and the size and shape of the tank(s). Here we will concern ourselves with the choice of front-end kit (i.e. the engine-bay components).
Multi-point Sequential Gas Injection Systems (SGIS) are the most appropriate type of LPG conversion for vehicles built after 1999. This is the point at which emission controls were tightened and we started to see lambda probes (oxygen sensors) fitted after the catalytic converters as well as before. It was also the point at which OBD2 (On-Board Diagnostics 2) became the norm.
Vehicles built before 1999 that have plastic inlet manifolds should also use SGI Systems.
So, that covers the vehicles that must use SGI Systems, but there are others that have the option to use them. Any water-cooled engine that has electronic petrol injection with individual injectors for each cylinder, and an ECU to control them, and a lambda probe in the exhaust could be converted using an SGI System.
There is an overriding consideration for any petrol-injected engine conversion. It concerns the location of the petrol injectors. An engine with petrol injectors in the inlet manifold (indirect injection) should not be a problem. However, if the injectors deliver petrol into the combustion chamber (direct injection), then special care must be taken to ensure that the petrol injectors do not suffer from over-heating when running on LPG. Each direct injection engine requires specific customisation of the fuel delivery system, and this is carried out by the manufacturer of the LPG system.
So, if you have a direct injection engine for conversion, you will need to check that a system is available for your vehicle and engine code.
SGI Systems work with the petrol ECU to run the engine as the ECU manufacturer intended.
Single-point induction systems work independently of the petrol ECU or carburettor.
There are 2 types of single-point induction system – open-loop and closed-loop. The open-loop type system is fairly basic, in that it has no automated way of measuring and adjusting fuelling as you drive. The closed-loop type system uses a lambda probe to determine if the fuelling is rich or lean and then automatically adjusts it.
For any conversion of an engine with soft valve seats, be sure to use a valve-saver system, such as FlashLube.