The EOBD (European On Board Diagnostic) is always active during the gas functioning. In case of failure of components of the gas system which affect the polluting emissions, the gas ECU instantaneously commands the switchback of the fuel to petrol and memorises the event. This can be read by the installer to formulate a correct diagnosis of the breakdown. The automatic switchback to petrol following the failure is displayed on the quadrant of the changeover switch (see paragraph “Display of change-over switch”).
Some versions of the control unit allow connecting to the car’s original OBD system (On-board diagnostics).
The Taurus retrofit system is activated/deactivated by simply pressing the special switch located on the changeover panel. The user can give two commands:
1. the change-over to petrol
2. the pre-selection of the changeover to gas.
The first command allows changing the engine fuel from gas to petrol. This is carried out instantaneously by the gas ECU and involves closing the solenoid valves for the gas interception, deactivating the gas electro-injectors, reactivating the petrol injectors and deactivating their emulation function.
The second command allows changing the fuel of the engine from petrol to gas. It is carried out by the gas ECU on condition that the temperature of the engine’s cooling liquid is higher than a pre-set value (changeover temperature). This guarantees complete gasification of the LPG, which is necessary for correctly supplying fuel to the engine and for respecting the limits of the polluting emissions established by the current standards. During the changeover, the gas electronic control opens the solenoid valves for the gas interception, activates the gas injectors, and deactivates and emulates the petrol injectors.
Therefore, upon changeover, the opening of the solenoid valves allows the liquid gas to flow in pressure from the tank towards the vaporizer. The pressure of the liquid LPG is reduced in the vaporizer with the subsequent vaporisation. This is completed by taking heat from the liquid of the heating circuit in the passenger compartment. The gaseous LPG is therefore taken to the electronic injection unit, which commanded by the gas ECU, determines the gas dosage to go to the engine. In any type of operating condition, the quantity injected is calculated by the gas ECU that processes the injection times of the petrol ECU (according to a master/slave operating scheme) and generates the command for opening the gas electro-injectors.