VSI stands for "vapour sequential injection", it points directly to the most important properties of the system. This second-generation gas injection system is based on a vapour LPG injection that is injected sequentially in the engine. Sequential means that the LPG injectors will inject the LPG in the sequence equal to that of the petrol injectors. This sequence in most applications is equal to the firing order of the ignition sequence of the engine, for example with a 4-cylinder engine this is normally 1-3-4-2. Sequential injection means that the amount of injected fuel per cylinder can be metered and timed individually.

VSI characterizes itself with a high level of integration into to the petrol management system. The two systems integrate as "master-slave". This means that the original petrol management ECM controls the amount of LPG injected via the LPG injectors into the engine. The VSI ECM only translates the relevant signals coming from the engine management system necessary for master /slave strategy. Following this strategy the petrol management system is the "master" and the VSI ECM the "slave". The advantage of this strategy: while driving on LPG the lambda control and OBD functions keep within the OE parameters, functioning correctly and controlled by the petrol management system. So when operating on LPG therefore, simulated signals are not necessary whilst operating on LPG.

There is one exception made for the petrol injector signals, while driving on LPG the petrol injector's are switched off to discontinue the petrol supply. To maintain the injection control signals it is necessary to simulate the petrol injectors to ensure the original ECM does not detect a fault code. Secondly when operating on LPG it is necessary to maintain a petrol injector control signal to measure the required fuel demand.

We already have proven this strategy for EOBD engines is successful with our first generation injection system YPS. The second generation injection system VSI has the ability to inject sequentially making it quicker and more accurate and large benefits can be gained in engine and emission performance.